Adhesives comprising crosslinker with (meth)acrylate group and olefin group and methods

ABSTRACT

There is provided an article having a release liner and a pressure sensitive adhesive composition disposed along a major surface of the release liner, where the pressure sensitive adhesive composition has at least 50 wt-% of polymerized units derived from alkyl meth(acrylate) monomer(s); and 0.2 to 15 wt-% of at least one crosslinking monomers comprising a (meth)acrylate group and a C 6 -C 20  olefin group, the olefin group being optionally substituted. In another embodiment, an adhesive composition is described comprising a syrup comprising i) a free-radically polymerizable solvent monomer; and ii) a solute (meth)acrylic polymer comprising polymerized units derived from one or more alkyl(meth)acrylate monomers; wherein the syrup comprises at least one crosslinking monomer or the (meth)acrylic solute polymer comprises polymerized units derived from at least one crosslinking monomer, the crosslinking monomer comprising a (meth)acrylate group and a C 6 -C 20  olefin group, the olefin group being optionally substituted.

BACKGROUND

As described in WO 2012/177337, there are two major crosslinkingmechanisms for acrylic adhesives: free-radical copolymerization ofmultifunctional ethylenically unsaturated groups with the othermonomers, and covalent or ionic crosslinking through the functionalmonomers, such as acrylic acid. Another method is the use of UVcrosslinkers, such as copolymerizable benzophenones or post-addedphotocrosslinkers, such as multifunctional benzophenones and triazines.In the past, a variety of different materials have been used ascrosslinking agents, e.g., polyfunctional acrylates, acetophenones,benzophenones, and triazines. The foregoing crosslinking agents,however, possess certain drawbacks which include one or more of thefollowing: high volatility; incompatibility with certain polymersystems; generation of undesirable color; requirement of a separatephotoactive compound to initiate the crosslinking reaction; and highsensitivity to oxygen. A particular issue for the electronics industryand other applications in which PSAs contact a metal surface is thegeneration of corrosive by-products and the generation of undesirablecolor.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying figures, in which:

FIG. 1 depicts the tan delta, the ratio of the shear loss modulus (G″)to the shear storage modulus (G′), as determined by dynamic mechanicalanalysis.

FIG. 2 illustrates an exemplary ultraviolet radiation curing chamberuseful in some exemplary embodiments of the present disclosure.

FIG. 3 illustrates an exemplary article including an ultravioletradiation cured coating according to some exemplary embodiments of thepresent disclosure.

While the above-identified drawings, which may not be drawn to scale,set forth various embodiments of the present disclosure, otherembodiments are also contemplated, as noted in the Detailed Description.In all cases, this disclosure describes the presently disclosedinvention by way of representation of exemplary embodiments and not byexpress limitations. It should be understood that numerous othermodifications and embodiments can be devised by those skilled in theart, which fall within the scope and spirit of this invention.

SUMMARY

Thus, industry would find advantage in alternative crosslinkers that aresubstantially free of halogens for use in pressure sensitive adhesives.There is also a need for articles having these adhesives disposed on amajor surface of a release liner that is substantially free of metalcatalyst.

In one aspect, the present disclosure provides an article comprising arelease liner and a pressure sensitive adhesive composition disposed ona major surface of the release liner, wherein the pressure sensitiveadhesive comprises at least 50 wt-% of polymerized units derived fromalkyl(meth)acrylate monomer(s); and 0.2 to 15 wt-% of at least onecrosslinking monomer comprising a (meth)acrylate group and a C₆-C₂₀olefin group, the olefin group being straight-chained or branched andoptionally substituted.

In some embodiments, the present disclosure provides articles such asthose according to the previously mention aspect in which the releaseliner is created by applying a layer comprising a(meth)acrylate-functional siloxane to a major surface of a substrate;and irradiating said layer, in a substantially inert atmospherecomprising no greater than 500 ppm oxygen, with a short wavelengthpolychromatic ultraviolet light source having at least one peakintensity at a wavelength of from about 160 nanometers to about 240nanometers to at least partially cure the layer, optionally wherein thelayer is at a curing temperature greater than 25° C.

In another aspect, the present disclosure provides an article comprisinga release liner and a pressure sensitive adhesive composition disposedon a major surface of the release liner, wherein the pressure sensitiveadhesive is a UV curable (meth)acrylic pressure sensitive adhesive thatis substantially free of halogens, and further wherein the release linercomprises a UV curable release layer on a major surface of a substrate.

In yet another aspect, the present disclosure provides an articlecomprising a release liner and a pressure sensitive adhesive compositiondisposed on a major surface of the release liner, wherein the pressuresensitive adhesive comprises at least 50 wt-% of polymerized unitsderived from alkyl(meth)acrylate monomer(s); and 0.2 to 15 wt-% of atleast one crosslinking monomer comprising a (meth)acrylate group and aC₆-C₂₀ olefin group, the olefin group being straight-chained or branchedand optionally substituted, and further wherein the release liner isderived by applying a layer comprising a (meth)acrylate-functionalsiloxane to a major surface of a substrate; and irradiating said layer,in a substantially inert atmosphere comprising no greater than 500 ppmoxygen, with a short wavelength polychromatic ultraviolet light sourcehaving at least one peak intensity at a wavelength of from about 160nanometers to about 240 nanometers to at least partially cure the layer,optionally wherein the layer is at a curing temperature greater than 25°C.

DETAILED DESCRIPTION

The present disclosure describes pressure sensitive adhesives (PSAs)prepared from crosslinkable (e.g. syrup) compositions, as well asarticles. The crosslinked pressure-sensitive adhesives provide asuitable balance of tack, peel adhesion, and shear holding power.Further, the storage modulus of the pressure sensitive adhesive at theapplication temperature, typically room temperature (25° C.), is lessthan 3×10⁵ dynes/cm at a frequency of 1 Hz. In some embodiments, theadhesive is a pressure sensitive adhesive at an application temperaturethat is greater than room temperature. For example, the applicationtemperature may be 30, 35, 40, 45, 50, 55, or 65° C. In this embodiment,the storage modulus of the pressure sensitive adhesive at roomtemperature (25° C.) is typically less than 3×10⁶ dynes/cm at afrequency of 1 Hz. In some embodiments, the storage modulus of thepressure sensitive adhesive at room temperature (25° C.) is less than2×10⁶ dynes/cm or 1×10⁶ dynes/cm at a frequency of 1 Hz.

Words of orientation such as “atop, “on,” “covering,” “uppermost,”“overlaying,” “underlying” and the like for describing the location ofvarious layers, refer to the relative position of a layer with respectto a horizontally-disposed, upwardly-facing substrate. It is notintended that the substrate, layers or articles encompassing thesubstrate and layers, should have any particular orientation in spaceduring or after manufacture.

“Layer” refers to any material or combination of materials on oroverlaying a substrate.

“Overcoat” or “overcoated” describes the position of a layer withrespect to a substrate or another layer of a multi-layer construction,means that the described layer is atop or overlaying the substrate oranother layer, but not necessarily adjacent to or contiguous with eitherthe substrate or the other layer.

The term “separated by” to describe the position of a layer with respectto another layer and the substrate, or two other layers, means that thedescribed layer is between, but not necessarily contiguous with, theother layer(s) and/or substrate.

“Syrup composition” refers to a solution of a solute polymer in one ormore solvent monomers, the composition having a viscosity from 100 to8,000 cPs at 25° C. The viscosity of the syrup is greater than theviscosity of the solvent monomer(s).

“alkyl” refers to straight-chained, branched, and cyclic alkyl groupsand includes both unsubstituted and substituted alkyl groups. Unlessotherwise indicated, the alkyl groups typically contain from 1 to 20carbon atoms. Examples of “alkyl” as used herein include, but are notlimited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl,t-butyl, isopropyl, n-octyl, 2-octyl, n-heptyl, ethylhexyl, cyclopentyl,cyclohexyl, cycloheptyl, adamantyl, and norbornyl, and the like. Unlessotherwise noted, alkyl groups may be mono- or polyvalent.

The term heteroalkyl refers to an alkyl group, as just defined, havingat least one catenary carbon atom (i.e. in-chain) replaced by a catenaryheteroatom such as O, S, or N.

The term olefin group refers to an unsaturated aliphaticstraight-chained, branched, or cyclic (i.e. unsubstituted) hydrocarbongroup having one or more double bonds. Those containing one double bondare commonly called alkenyl groups. In some embodiments, the cyclicolefin group comprises less than 10 or 8 carbon atoms, such as in thecase of cyclohexenyl. In some embodiments, the olefin group may furthercomprise substituents as will subsequently be described. The olefingroup is typically monovalent.

“Renewable resource” refers to a natural resource that can bereplenished within a 100 year time frame. The resource may bereplenished naturally or via agricultural techniques. The renewableresource is typically a plant (i.e. any of various photosyntheticorganisms that includes all land plants, inclusive of trees), organismsof Protista such as seaweed and algae, animals, and fish. They may benaturally occurring, hybrids, or genetically engineered organisms.Natural resources such as crude oil, coal, and peat which take longerthan 100 years to form are not considered to be renewable resources.

“Catenated heteroatom” means an atom other than carbon (for example,oxygen, nitrogen, or sulfur) that replaces one or more carbon atoms in acarbon chain (for example, so as to form a carbon-heteroatom-carbonchain or a carbon-heteroatom-heteroatom-carbon chain);

“Cure” means conversion to a crosslinked polymer network (for example,through catalysis);

“Fluoro-” (for example, in reference to a group or moiety, such as inthe case of “fluoroalkylene” or “fluoroalkyl” or “fluorocarbon”) or“fluorinated” means only partially fluorinated such that there is atleast one carbon-bonded hydrogen atom;

“Fluorochemical” means fluorinated or perfluorinated;

“Heteroorganic” means an organic group or moiety (for example, an alkylor alkylene group) containing at least one heteroatom (preferably, atleast one catenated heteroatom);

“Hydrosilyl” refers to a monovalent moiety or group comprising a siliconatom directly bonded to a hydrogen atom (for example, the hydrosilylmoiety can be of formula —Si(R)_(3-p)(H)_(p), where p is an integer of1, 2, or 3 and R is a hydrolyzable or non-hydrolyzable group(preferably, non-hydrolyzable) such as alkyl or aryl);

“Hydroxysilyl” refers to a monovalent moiety or group comprising asilicon atom directly bonded to a hydroxyl group (for example, thehydroxysilyl moiety can be of formula —Si(R)_(3-p)(OH)_(p) where p is aninteger of 1, 2, or 3 and R is a hydrolyzable or non-hydrolyzable group(preferably, non-hydrolyzable) such as alkyl or aryl);

“Isocyanato” means a monovalent group or moiety of formula —NCO;

“Mercapto” means a monovalent group or moiety of formula —SH;

“Oligomer” means a molecule that comprises at least two repeat units andthat has a molecular weight less than its entanglement molecular weight;such a molecule, unlike a polymer, exhibits a significant change inproperties upon the removal or addition of a single repeat unit;

“Oxy” means a divalent group or moiety of formula —O—; and

“Perfluoro-” (for example, in reference to a group or moiety, such as inthe case of “perfluoroalkylene” or “perfluoroalkyl” or“perfluorocarbon”) or “perfluorinated” means completely fluorinated suchthat, except as may be otherwise indicated, there are no carbon-bondedhydrogen atoms replaceable with fluorine.

“Intensity peak” refers to a local maximum in an emission spectrum for aUV radiation source when plotted as emission intensity as a function ofemission wavelength. The emission spectrum may have one or moreintensity peaks over the wavelength range covered by the emissionspectrum. Thus, an intensity peak need not correspond to the maximumemission intensity peak over the entire wavelength range covered by theemission spectrum.

“Polychromatic UV radiation,” “polychromatic UV light,” “shortwavelength polychromatic UV radiation,” and “short wavelengthpolychromatic UV light” all refer to ultraviolet radiation or lighthaving an emission wavelength of 400 nm or less wherein the emissionspectrum includes at least two intensity peaks, with at least oneintensity peak occurring at no greater than 240 nanometers (nm).

“Substantially inert atmosphere” refers to an atmosphere having anoxygen content of no greater than 500 ppm.

“Substantially free of halogens” refers to a pressure sensitive adhesivein composition which a substance containing a halogen atom is not usedintentionally as a main component.

“Substantially free of metal catalyst” refers to a release compositionin which a substance containing a metal catalyst is not usedintentionally as a main component.

“(Meth)acrylic” or “(meth)acrylic-functional” includes materials thatinclude one or more ethylenically unsaturated acrylic- and/ormethacrylic-functional groups, e.g. -AC(O)C(R)═CH₂, preferably wherein Ais O, S or NR′, wherein R′ is a hydrogen atom or a hydrocarbon group;and R is a 1-4 carbon lower alkyl group, H or F. Herein,“(meth)acryloyl” is inclusive of (meth)acrylate and (meth)acrylamide.Herein, “(meth)acrylic” includes both methacrylic and acrylic.

Herein, “(meth)acrylate” includes both methacrylate and acrylate.

“Siloxane” includes any chemical compound composed of units of —O—Si—O—and having the generalized formula R′₂SiO, wherein R′ is a hydrogen atomor a hydrocarbon group.

“(Co)polymer” or “(co)polymeric” includes homopolymers and copolymers,as well as homopolymers or copolymers that may be formed in a miscibleblend, e.g., by coextrusion or by reaction, including, e.g.,transesterification. The term “copolymer” includes random, block, graft,and star copolymers.

“Cure” or “curable” refers to a process that causes a chemical change,e.g., a reaction to solidify a layer or increase its viscosity.

“Cured (co)polymer layer” or “cured (co)polymer” includes bothcross-linked and uncross-linked (co)polymers.

“Cross-linked” (co)polymer refers to a (co)polymer whose (co)polymerchains are joined together by covalent chemical bonds, usually viacross-linking molecules or groups, to form a network (co)polymer. Across-linked (co)polymer is generally characterized by insolubility, butmay be swellable in the presence of an appropriate solvent.

“Unaged peel adhesion” refers to peel adhesion measured according to therelease test described herein on a release surface maintained at atemperature of no more than 25° C. at no more than 75% relative humidityfor no more than 24 hours before the measurement. Preferably, the unagedpeel adhesion is measured on a release surface within one hour ofpreparation of the release surface.

“Aged peel adhesion” refers to peel adhesion measured according to therelease test described herein on a release surface aged for at leastseven days at 90° C. and 90% relative humidity.

When a group is present more than once in a formula described herein,each group is “independently” selected unless specified otherwise.

The adhesive comprises a (meth)acrylic polymer prepared from one or moremonomers common to acrylic adhesives, such as a (meth)acrylic estermonomers (also referred to as (meth)acrylate acid ester monomers andalkyl(meth)acrylate monomers) optionally in combination with one or moreother monomers such as acid-functional ethylenically unsaturatedmonomers, non-acid-functional polar monomers, and vinyl monomers.

The (meth)acrylic polymer comprises one or more (meth)acrylate estermonomers derived from a (e.g. non-tertiary) alcohol containing from 1 to14 carbon atoms and preferably an average of from 4 to 12 carbon atoms.

Examples of monomers include the esters of either acrylic acid ormethacrylic acid with non-tertiary alcohols such as ethanol, 1-propanol,2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol,2-methyl-1-butanol, 3-methyl-1-butanol, 1-hexanol, 2-hexanol,2-methyl-1-pentanol, 3-methyl-1-pentanol, 2-ethyl-1-butanol,3,5,5-trimethyl-1-hexanol, 3-heptanol, 1-octanol, 2-octanol,isooctylalcohol, 2-ethyl-1-hexanol, 1-decanol, 2-propylheptanol,1-dodecanol, 1-tridecanol, 1-tetradecanol, and the like. In someembodiments, a preferred (meth)acrylate ester monomer is the ester of(meth)acrylic acid with isooctyl alcohol.

In some favored embodiments, the monomer is the ester of (meth)acrylicacid with an alcohol derived from a renewable source. A suitabletechnique for determining whether a material is derived from a renewableresource is through ¹⁴C analysis according to ASTM D6866-10, asdescribed in US2012/0288692. The application of ASTM D6866-10 to derivea “bio-based content” is built on the same concepts as radiocarbondating, but without use of the age equations. The analysis is performedby deriving a ratio of the amount of organic radiocarbon (¹⁴C) in anunknown sample to that of a modern reference standard. The ratio isreported as a percentage with the units “pMC” (percent modern carbon).

One suitable monomer derived from a renewable source is2-octyl(meth)acrylate, as can be prepared by conventional techniquesfrom 2-octanol and (meth)acryloyl derivatives such as esters, acids andacyl halides. The 2-octanol may be prepared by treatment of ricinoleicacid, derived from castor oil, (or ester or acyl halide thereof) withsodium hydroxide, followed by distillation from the co-product sebacicacid. Other (meth)acrylate ester monomers that can be renewable arethose derived from ethanol and 2-methyl butanol. In some embodiments,the (e.g. pressure sensitive) adhesive composition (e.g. (meth)acrylicpolymer and/or free-radically polymerizable solvent monomer) comprises abio-based content of at least 25, 30, 35, 40, 45, or 50 wt-% using ASTMD6866-10, method B. In other embodiments, the (e.g. pressure sensitive)adhesive composition comprises a bio-based content of at least 55, 60,65, 70, 75, or 80 wt-%. In yet other embodiments, the (e.g. pressuresensitive) adhesive composition comprises a bio-based content of atleast 85, 90, 95, 96, 97, 99 or 99 wt-%.

The (e.g. pressure sensitive) adhesive (e.g. (meth)acrylic polymerand/or solvent monomer) comprises one or more low Tg (meth)acrylatemonomers, having a T_(g) no greater than 10° C. when reacted to form ahomopolymer. In some embodiments, the low Tg monomers have a T_(g) nogreater than 0° C., no greater than −5° C., or no greater than −10° C.when reacted to form a homopolymer. The T_(g) of these homopolymers isoften greater than or equal to −80° C., greater than or equal to −70°C., greater than or equal to −60° C., or greater than or equal to −50°C. The T_(g) of these homopolymers can be, for example, in the range of−80° C. to 20° C., −70° C. to 10° C., −60° C. to 0° C., or −60° C. to−10° C.

The low Tg monomer may have the formula

H₂C═CR¹C(O)OR⁸

wherein R¹ is H or methyl and R⁸ is an alkyl with 1 to 22 carbons or aheteroalkyl with 2 to 20 carbons and 1 to 6 heteroatoms selected fromoxygen or sulfur. The alkyl or heteroalkyl group can be linear,branched, cyclic, or a combination thereof.

Exemplary low Tg monomers include for example ethyl acrylate, n-propylacrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate,n-pentyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-methylbutylacrylate, 2-ethylhexyl acrylate, 4-methyl-2-pentyl acrylate, n-octylacrylate, 2-octyl acrylate, isooctyl acrylate, isononyl acrylate, decylacrylate, isodecyl acrylate, lauryl acrylate, isotridecyl acrylate,octadecyl acrylate, and dodecyl acrylate.

Low Tg heteroalkyl acrylate monomers include, but are not limited to,2-methoxyethyl acrylate and 2-ethoxyethyl acrylate.

In some embodiments, the (e.g. pressure sensitive) adhesive (e.g.(meth)acrylic polymer and/or free radically polymerizable solventmonomer) comprises low Tg monomer(s) having an alkyl group with 6 to 20carbon atoms. In some embodiments, the low Tg monomer has an alkyl groupwith 7 or 8 carbon atoms. Exemplary monomers include, but are notlimited to, 2-ethylhexyl methacrylate, isooctyl methacrylate, n-octylmethacrylate, 2-octyl methacrylate, isodecyl methacrylate, and laurylmethacrylate. Likewise, some heteroalkyl methacrylates such as 2-ethoxyethyl methacrylate can also be used.

In some embodiments, the (e.g. pressure sensitive) adhesive (e.g.(meth)acrylic polymer and/or solvent monomer) comprises a high T_(g)monomer, having a T_(g) greater than 10° C. and typically of at least15° C., 20° C. or 25° C., and preferably at least 50° C. Suitable highTg monomers include, for example, t-butyl acrylate, methyl methacrylate,ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate,isobutyl methacrylate, s-butyl methacrylate, t-butyl methacrylate,stearyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate,isobornyl acrylate, isobornyl methacrylate, norbornyl(meth)acrylate,benzyl methacrylate, 3,3,5 trimethylcyclohexyl acrylate, cyclohexylacrylate, N-octyl acrylamide, and propyl methacrylate or combinations.

In some embodiments, the (meth)acrylic polymer is a homopolymer. Inother embodiments, the (meth)acrylic polymer is a copolymer. Unlessspecified otherwise, the term polymer refers to both a homopolymer andcopolymer.

The T_(g) of the copolymer may be estimated by use of the Fox equation,based on the T_(g)s of the constituent monomers and the weight percentthereof.

The alkyl(meth)acrylate monomers are typically present in the(meth)acrylic polymer in an amount of at least 85, 86, 87, 88, 89, or 90up to 95, 96, 97, 98, or 99 parts by weight, based on 100 parts byweight of the total monomer or polymerized units. When high T_(g)monomers are included in a pressure sensitive adhesive, the adhesive mayinclude at least 5, 10, 15, 20, to 30 parts by weight of such high Tgmonomer(s). When the (e,g. pressure sensitive) adhesive composition isfree of unpolymerized components, such as tackifier, silica, and glassbubbles, the parts by weight of the total monomer or polymerized unitsis approximately the same as the wt-% present in the total adhesivecomposition. However, when the (e.g. pressure sensitive) adhesivecomposition comprises such unpolymerized components, the (e.g. pressuresensitive) adhesive composition can comprises substantially lessalkyl(meth)acrylate monomer(s) and crosslinking monomer. The (e.g.pressure sensitive) adhesive composition comprises at least 50 wt-% ofpolymerized units derived from alkyl(meth)acrylate monomers. In someembodiments, the pressure sensitive adhesive composition comprises atleast 50, 55, 60, 65, 70, 75, 80, 85, or 90 parts by weight, based on100 parts by weight of the total monomer (or wt-% of the total adhesivecomposition) of one or more low Tg monomers. For embodied methodswherein the adhesive is not a pressure sensitive adhesive, the adhesivemay comprise 50, 55, 60, 65, 70, 75, 80, 85, or 90 parts by weight,based on 100 parts by weight of the total monomer (or wt-% of the totaladhesive composition) of one or more high Tg monomers. The (meth)acrylicpolymer may optionally comprise an acid functional monomer (a subset ofhigh Tg monomers), where the acid functional group may be an acid perse, such as a carboxylic acid, or a portion may be salt thereof, such asan alkali metal carboxylate. Useful acid functional monomers include,but are not limited to, those selected from ethylenically unsaturatedcarboxylic acids, ethylenically unsaturated sulfonic acids,ethylenically unsaturated phosphonic acids, and mixtures thereof.Examples of such compounds include those selected from acrylic acid,methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconicacid, maleic acid, oleic acid, β-carboxyethyl(meth)acrylate,2-sulfoethyl methacrylate, styrene sulfonic acid,2-acrylamido-2-methylpropanesulfonic acid, vinylphosphonic acid, andmixtures thereof.

Due to their availability, acid functional monomers are generallyselected from ethylenically unsaturated carboxylic acids, i.e.(meth)acrylic acids. When even stronger acids are desired, acidicmonomers include the ethylenically unsaturated sulfonic acids andethylenically unsaturated phosphonic acids. In some embodiments, theacid functional monomer is generally used in amounts of 0.5 to 15 partsby weight, preferably 0.5 to 10 parts by weight, based on 100 parts byweight total monomer or polymerized units. In some embodiments, the(meth)acrylic polymer and/or PSA comprises less than 1.0, 0.9, 0.8, 0.7,0.6, 0.5, 0.4, 0.3, 0.2, 0.1 or 0 wt-% of polymerized units derived fromacid-functional monomers such as acrylic acid.

The (meth)acrylic copolymer may optionally comprise other monomers suchas a non-acid-functional polar monomer. Representative examples ofsuitable polar monomers include but are not limited to2-hydroxyethyl(meth)acrylate; N-vinylpyrrolidone; N-vinylcaprolactam;acrylamide; mono- or di-N-alkyl substituted acrylamide; t-butylacrylamide; dimethylaminoethyl acrylamide; N-octyl acrylamide;poly(alkoxyalkyl)(meth)acrylates including2-(2-ethoxyethoxy)ethyl(meth)acrylate, 2-ethoxyethyl(meth)acrylate,2-methoxyethoxyethyl(meth)acrylate, 2-methoxyethyl methacrylate,polyethylene glycol mono(meth)acrylates; alkyl vinyl ethers, includingvinyl methyl ether; and mixtures thereof. Preferred polar monomersinclude those selected from the group consisting of2-hydroxyethyl(meth)acrylate and N-vinylpyrrolidinone. Thenon-acid-functional polar monomer may be present in amounts of 0 to 10or 20 parts by weight, or 0.5 to 5 parts by weight, based on 100 partsby weight total monomer. In some embodiments, the (meth)acrylic polymerand/or PSA comprises less than 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3,0.2, 0.1 or 0 wt-% of polymerized units derived from non-acid polarmonomers.

When used, vinyl monomers useful in the (meth)acrylate polymer includevinyl esters (e.g., vinyl acetate and vinyl propionate), styrene,substituted styrene (e.g., α-methyl styrene), vinyl halide, and mixturesthereof. As used herein vinyl monomers are exclusive of acid functionalmonomers, acrylate ester monomers and polar monomers. Such vinylmonomers are generally used at 0 to 5 parts by weight, preferably 1 to 5parts by weight, based on 100 parts by weight total monomer orpolymerized units. In some embodiments, the (meth)acrylic polymer and/orPSA comprises less than 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1or 0 wt-% of polymerized units derived from vinyl monomers.

In some embodiments, the polymer contains no allyl ether, vinyl ether orvinyl ester monomer units.

The adhesive further comprises a crosslinking monomer comprising a(meth)acrylate group and aC₆-C₂₀ olefin group. The olefin groupcomprises at least one hydrocarbon unsaturation. In some embodiments,the olefin group comprises substitutents. The crosslinking monomer mayhave the formula

R1 is H or CH₃,

L is an optional linking group; andR2 is a C₆-C₂₀ olefin group, the olefin group being optionallysubstituted.

For embodiments wherein the crosslinking monomer comprises a (e.g.divalent) linking group, the linking group (i.e. L) typically has amolecular weight no greater than 1000 g/mole and in some embodiments nogreater than 500 g/mole, 400 g/mole, 300 g/mole, 200 g/mole, 100 g/mole,or 50 g/mole.

In some embodiments, the crosslinking monomer comprises a (meth)acrylategroup and an optionally substituted C₆-C₂₀ olefin group comprising aterminal hydrocarbon unsaturation. In this embodiment the hydrocarbonunsaturation has the formula:

R³C═CR⁴R⁵

wherein R⁴ and R⁵ are H and R³ is H or (e.g. C₁-C₄) alkyl.Undecenyl(meth)acrylate includes such terminal unsaturation.

In other embodiments, the crosslinking monomer comprises a(meth)acrylate group and an optionally substituted C₆-C₂₀ olefin groupcomprising at least one hydrocarbon unsaturation in the backbone of theoptionally substituted C₆-C₂₀ olefin group. In this embodiment, thehydrocarbon unsaturation has the formula:

R³C═CR⁴R⁵

wherein R⁴ and R⁵ are independently alkyl and R³ is H or (e.g. C₁-C₄)alkyl. In some embodiments, R⁴ and R⁵ are each methyl. In thisembodiment, R⁴ or R⁵ is the terminal alkyl group of the C₆-C₂₀ olefingroup. Citronellyl(meth)acrylate, geraniol(meth)acrylate andfarnesol(meth)acrylate include a hydrocarbon unsaturation of this type.

In some embodiments, the crosslinking monomer comprises a (meth)acrylategroup and an optionally substituted C₆-C₂₀ olefin group comprising twoor more hydrocarbon unsaturations in the backbone. Some illustrativecrosslinking monomers include for example geraniol(meth)acrylate (e.g.3,7-dimethylocta-2,6-dienyl]prop-2-enoate) and farnesol(meth)acrylate(e.g. 3,7,11-trimethyldodeca-2,6,10-trienyl]prop-2-enoate).

In yet another embodiment of a hydrocarbon unsaturation in the backboneof the optionally substituted C₆-C₂₀ olefin group, R³ and R⁴ areindependently H or (e.g. C₁-C₄) alkyl and R⁵ is a terminal alkyl grouphaving up to 18 carbon atoms. Oleyl(meth)acrylate includes a hydrocarbonunsaturation of this type.

In typical embodiments, the substituted C₆-C₂₀ olefin group does notcomprise a carbonyl group. Thus, the (meth)acrylate group is the onlygroup of the crosslinking monomer that comprises a carbonyl group. Thus,the crosslinking monomer is free of other groups that comprise acarbonyl such as an aldehyde, ketone, carboxylic acid, ester, amide,enone, acryl halide, acid anhydride, and imide. Hence, the crosslinkingmonomer comprises or consists of two types of polymerizable functionalgroups, i.e. a single (meth)acrylate group and one or more hydrocarbonunsaturations.

The optionally substituted C₆-C₂₀ olefin group may be a straight-chain,branched, or cyclic. Further, the hydrocarbon unsaturation may be at anyposition.

When the crosslinking monomer comprises a single hydrocarbonunsaturation, the unsubstituted C₆-C₂₀ olefin group may be characterizedas an alkenyl group. In some embodiments, the alkenyl group has astraight chain. In some embodiments, the alkenyl group has branchedchain, commonly comprising pendent methyl groups bonded to a straightchain.

Some illustrative crosslinking monomers comprising an alkenyl groupinclude citronellyl(meth)acrylate, 3-cyclohexene methyl(meth)acrylate,undecenyl(meth)acrylate, and oleyl acrylate. Other C₆-C₂₀ alkenyl groupsinclude 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, 5-hexenyl,1-methyl-1-pentenyl, 2-methyl-1-pentenyl, 3-methyl-1-pentenyl,4-methyl-1-pentenyl, 1-methyl-2-pentenyl, 2-methyl-2-pentenyl,3-methyl-2-pentenyl, 4-methyl-2-pentenyl, 1-methyl-3-pentenyl,2-methyl-3-pentenyl, 3-methyl-3-pentenyl, 4-methyl-3-pentenyl,1-methyl-4-pentenyl, 2-methyl-4-pentenyl, 3-methyl-4-pentenyl,4-methyl-4-pentenyl; 1,1-dimethyl-2-butenyl; 1,1-dimethyl-3-butenyl;1,2-dimethyl-1-butenyl; 1,2-dimethyl-2-butenyl; 1,2-dimethyl-3-butenyl;1,3-dimethyl-1-butenyl; 1,3-dimethyl-2-butenyl; 1,3-dimethyl-3-butenyl;2,2-dimethyl-3-butenyl; 2,3-dimethyl-1-butenyl; 2,3-dimethyl-2-butenyl;2,3-dimethyl-3-butenyl; 3,3-dimethyl-1-butenyl; 3,3-dimethyl-2-butenyl;1,1,2-trimethyl-2-propenyl; and also the isomers of heptenyl, octenyl,and nonenyl.

Cyclic alkenyl groups included cyclohexenyl as well as dicyclopentenyl.

Provided that the C₆-C₂₀ olefin group comprises at least one hydrocarbonunsaturation, the C₆-C₂₀ olefin group may optionally comprisesubstituents. The substituents are chosen such that the crosslinkingmonomer comprises at least one hydrocarbon unsaturation available forcrosslinking, as evident by a measurable and preferably substantialincrease in shear values.

In some embodiments, the C₆-C₂₀ olefin group comprises pendentsubstituents. For example, when the C₆-C₂₀ olefin group comprises two ormore hydrocarbon unsaturations, one or more of the additionalhydrocarbon unsaturations can be reacted to append pendent substituentsonto the C₆-C₂₀ olefin group backbone.

In other embodiments, the C₆-C₂₀ olefin group can comprise substituentssuch as a heteroatom (e.g. oxygen) or a (e.g. divalent) linking group(i.e. “L”) between the (meth)acrylate group and C₆-C₂₀ olefin group. Forexample, the starting alcohol can be chain extended before reacting onthe (meth)acrylate group. In some embodiments, the starting alcohol ischain extended with one or more alkylene oxide groups, such as ethyleneoxide, propylene oxide, and combinations thereof. One illustrativecrosslinking monomer of this type is the ester of (meth)acrylic acid ofan ethoxylated and/or propoxylated unsaturated fatty alcohol. Some ofsuch ethoxylated and/or propoxylated unsaturated fatty alcohols arecommercially available as non-ionic surfactants. Thus, L comprises orconsists of alkylene (e.g. ethylene) oxide repeat units. Oneillustrative fatty alcohol of this type is available from Croda as “BrijO2”. Such ethoxylated alcohol comprises a mixture of molecules (whereinn is 1 or 2) having the general formula

C₁₈H₃₅(OCH₂CH₂)_(n)OH.

The crosslinking monomers can be prepared by reacting the correspondingalcohol with acryloyl chloride, methylene chloride and triethylamine, ora combination thereof, such as set forth in the examples. Thecrosslinking monomers can also be prepared by direct esterification withacrylic acid.

The concentration of crosslinking monomer comprising a (meth)acrylategroup and an optionally substituted C₆-C₂₀ olefin group is typically atleast 0.1, 0.2, 0.3, 0.4 or 0.5 wt-% and can range up to 10, 11, 12, 13,14, or 15 wt-% of the (e.g. pressure sensitive) adhesive composition.However, as the concentration of such crosslinking monomer increases,the peel adhesion (180° to stainless steel) can decrease. Thus, intypically embodiments, the concentration of crosslinking monomercomprising a (meth)acrylate group and an optionally substituted C₆-C₂₀olefin group is no greater than 9, 8, 7, 6, or 5 wt-% and in somefavored embodiments, no greater than 4, 3, 2, or 1 wt-%.

In some embodiments, the crosslinking monomer comprises a branchedC₆-C₂₀ having less than 18, or 16, or 14, or 12 carbon atoms, such as inthe case of citronellyl acrylate and geraniol acrylate. In thisembodiment, a pressure sensitive adhesive can be obtained having highshear values (i.e. greater than 10,000 minutes at 70° C.) in combinationwith high adhesion with as little as 0.5 wt-% of such crosslinkingmonomer. As the chain length of the branched C₆-C₂₀ group increases, theamount of crosslinking monomer needed to provide the same number ofcrosslinks increases. For example, in the case of farnesol acrylate atleast 0.7 wt-% or 0.8 wt-% resulted in high shear values. In the case ofcyclic C₆-C₂₀ olefin groups, such as in the case of cyclohexane methylacrylate, at least 2, 3, 4, or 5 wt-% resulted in high shear values. Inthe case of crosslinking monomers comprising a straight-chain C₆-C₂₀such as in the case of undecenyl acrylate and oleyl acrylate, high shearvalues in combination with high adhesion was obtained with about 1 wt-%.Lower concentrations of undecenyl acrylate and optionally substitutedoleyl acrylate are surmised to also provide a good balance ofproperties.

The (e.g. pressure sensitive) adhesive composition may comprise a singlecrosslinking monomer comprising a (meth)acrylate group and (optionallysubstituted) C₆-C₂₀ olefin group or a combination of two or more of suchcrosslinking monomers. Further, the crosslinking monomer may comprisetwo or more isomers of the same general structure.

In favored embodiments, the crosslinked adhesive composition compriseshigh shear values to stainless steel or orange peel drywall, i.e.greater than 10,000 minutes at 70° C., as determined according to thetest methods described in the examples. The crosslinked pressuresensitive adhesive can exhibit a variety of peel adhesion valuesdepending on the intended end use. In some embodiments, the 180° degreepeel adhesion to stainless steel is least 15 N/dm. In other embodiments,the 180° degree peel adhesion to stainless steel is least 20, 25, 30,35, 40, 45, 50, 55, 60, 65, 70, or 75 N/dm. The 180° degree peeladhesion to stainless steel is typically no greater than 150 or 100N/dm. Such peel adhesive values are also attainable when adhered toother substrates.

In some embodiments, such as in the case of optionally substitutedcitronellyl(meth)acrylate and oleyl(meth)acrylate, the crosslinkingmonomer is a bio-based material. Thus, the use of such crosslinkingmonomer is amenable to increasing the total content of biobased materialof the adhesive. Further, since the crosslinking monomer comprises anolefin group comprising at least 6 carbon atoms, when the hydrocarbonunsaturation does not crosslink, the crosslinking monomer can serve thefunction of a low Tg monomer. This can be amenable to utilizing higherconcentrations of such crosslinking monomer. Further, the crosslinkingmonomer does not form corrosive by-products and has good colorstability. In some embodiments, the b* of the adhesive after exposure toUV or heat, as described in greater detail in the test method describedin the examples, is less than 1 or 0.9, or 0.8, or 0.7, or 0.6, or 0.5,or 0.4, or 0.3. In some embodiments, the b* of the adhesive afterexposure to UV and heat, as described in greater detail in the testmethod described in the examples, is less than 2, or 1.5, or 1, or 0.9,or 0.8, or 0.7, or 0.6, or 0.5, or 0.4, or 0.3.

The (e.g. pressure sensitive) adhesive may optionally comprise anothercrosslinker in addition to the crosslinker having a (meth)acrylate groupand optionally substituted C₆-C₂₀ olefin group. In some embodiments, the(e.g. pressure sensitive) adhesive comprises a multifunctional(meth)acrylate.

Examples of useful multifunctional (meth)acrylate include, but are notlimited to, di(meth)acrylates, tri(meth)acrylates, andtetra(meth)acrylates, such as 1,6-hexanediol di(meth)acrylate,poly(ethylene glycol)di(meth)acrylates, polybutadiene di(meth)acrylate,polyurethane di(meth)acrylates, and propoxylated glycerintri(meth)acrylate, and mixtures thereof.

Generally the multifunctional (meth)acrylate is not part of the originalmonomer mixture, but added subsequently after the formation of the(meth)acrylic polymer. If used, the multifunctional (meth)acrylate istypically used in an amount of at least 0.01, 0.02, 0.03, 0.04, or 0.05up to 1, 2, 3, 4, or 5 parts by weight, relative to 100 parts by weightof the total monomer content.

In some embodiments, the (e.g. pressure sensitive) adhesive may furthercomprise a chlorinated triazine crosslinking compound. The triazinecrosslinking agent may have the formula.

wherein R₁, R₂, R₃ and R₄ of this triazine crosslinking agent areindependently hydrogen or alkoxy group, and 1 to 3 of R₁, R₂, R₃ and R₄are hydrogen. The alkoxy groups typically have no greater than 12 carbonatoms. In favored embodiments, the alkoxy groups are independentlymethoxy or ethoxy. One representative species is2,4,-bis(trichloromethyl)-6-(3,4-bis(methoxy)phenyl)-triazine. Suchtriazine crosslinking compounds are further described in U.S. Pat. No.4,330,590.

In some embodiments, the (e.g. pressure sensitive) adhesive comprisespredominantly (greater than 50%, 60%, 70%, 80%, or 90% of the totalcrosslinks) or exclusively crosslinks from the crosslinking monomer thatcomprises a (meth)acrylate group and an optionally substituted C₆-C₂₀olefin group. In such embodiment, the (e.g. pressure sensitive) adhesivemay be free of other crosslinking compounds, particularly aziridinecrosslinkers, as well as multifunctional (meth)acrylate crosslinkers,chlorinated triazine crosslinkers and melamine crosslinkers.

The (meth)acrylic copolymers and adhesive composition can be polymerizedby various techniques including, but not limited to, solventpolymerization, dispersion polymerization, solventless bulkpolymerization, and radiation polymerization, including processes usingultraviolet light, electron beam, and gamma radiation. The monomermixture may comprise a polymerization initiator, especially a thermalinitiator or a photoinitiator of a type and in an amount effective topolymerize the comonomers.

A typical solution polymerization method is carried out by adding themonomers, a suitable solvent, and an optional chain transfer agent to areaction vessel, adding a free radical initiator, purging with nitrogen,and maintaining the reaction vessel at an elevated temperature (e.g.about 40 to 100° C.) until the reaction is complete, typically in about1 to 20 hours, depending upon the batch size and temperature. Examplesof typical solvents include methanol, tetrahydrofuran, ethanol,isopropanol, acetone, methyl ethyl ketone, methyl acetate, ethylacetate, toluene, xylene, and an ethylene glycol alkyl ether. Thosesolvents can be used alone or as mixtures thereof.

Useful initiators include those that, on exposure to heat or light,generate free-radicals that initiate (co)polymerization of the monomermixture. The initiators are typically employed at concentrations rangingfrom about 0.0001 to about 3.0 parts by weight, preferably from about0.001 to about 1.0 parts by weight, and more preferably from about 0.005to about 0.5 parts by weight of the total monomer or polymerized units.

Suitable initiators include but are not limited to those selected fromthe group consisting of azo compounds such as VAZO 64(2,2′-azobis(isobutyronitrile)), VAZO 52(2,2′-azobis(2,4-dimethylpentanenitrile)), and VAZO 67(2,2′-azobis-(2-methylbutyronitrile)) available from E.I. du Pont deNemours Co., peroxides such as benzoyl peroxide and lauroyl peroxide,and mixtures thereof. The preferred oil-soluble thermal initiator is(2,2′-azobis-(2-methylbutyronitrile)). When used, initiators maycomprise from about 0.05 to about 1 part by weight, preferably about 0.1to about 0.5 part by weight based on 100 parts by weight of monomercomponents in the pressure sensitive adhesive.

The polymers prepared from solution polymerization have pendentunsaturated groups that can be crosslinked by a variety of methods.These include addition of thermal or photo initiators followed by heator UV exposure after coating. The polymers may also be crosslinked byexposure to electron beam or gamma irradiation.

One method of preparing (meth)acrylic polymers includes partiallypolymerizing monomers to produce a syrup composition comprising thesolute (meth)acrylic polymer and unpolymerized solvent monomer(s). Theunpolymerized solvent monomer(s) typically comprises the same monomer asutilized to produce the solute (meth)acrylic polymer. If some of themonomers were consumed during the polymerization of the (meth)acrylicpolymer, the unpolymerized solvent monomer(s) comprises at least some ofthe same monomer(s) as utilized to produce the solute (meth)acrylicpolymer. Further, the same monomer(s) or other monomer(s) can be addedto the syrup once the (meth)acrylic polymer has been formed. Partialpolymerization provides a coatable solution of the (meth)acrylic solutepolymer in one or more free-radically polymerizable solvent monomers.The partially polymerized composition is then coated on a suitablesubstrate and further polymerized.

In some embodiments, the crosslinking monomer is added to the monomer(s)utilized to form the (meth)acrylic polymer. Alternatively or in additionthereto, the crosslinking monomer may be added to the syrup after the(meth)acrylic polymer has been formed. The (meth)acrylate group of thecrosslinker and other (e.g. (meth)acrylate) monomers utilized to formthe (meth)acrylic polymer preferentially polymerize forming an acrylicbackbone with the pendent C₆-C₂₀ olefin group. Without intending to bebound by theory, it is surmised that at least a portion of thecarbon-carbon double bonds of the pendent C₆-C₂₀ olefin group crosslinkwith each other during radiation curing of the syrup. Other reactionmechanisms may also occur.

The syrup method provides advantages over solvent or solutionpolymerization methods; the syrup method yielding higher molecularweight materials. These higher molecular weights increase the amount ofchain entanglements, thus increasing cohesive strength. Also, thedistance between cross-links can be greater with high molecular syruppolymer, which allows for increased wet-out onto a surface.

Polymerization of the (meth)acrylate solvent monomers can beaccomplished by exposing the syrup composition to energy in the presenceof a photoinitiator. Energy activated initiators may be unnecessarywhere, for example, ionizing radiation is used to initiatepolymerization. Typically, a photoinitiator can be employed in aconcentration of at least 0.0001 part by weight, preferably at least0.001 part by weight, and more preferably at least 0.005 part by weight,relative to 100 parts by weight of the syrup.

A preferred method of preparation of the syrup composition isphotoinitiated free radical polymerization. Advantages of thephotopolymerization method are that 1) heating the monomer solution isunnecessary and 2) photoinitiation is stopped completely when theactivating light source is turned off. Polymerization to achieve acoatable viscosity may be conducted such that the conversion of monomersto polymer is up to about 30%. Polymerization can be terminated when thedesired conversion and viscosity have been achieved by removing thelight source and by bubbling air (oxygen) into the solution to quenchpropagating free radicals. The solute polymer(s) may be preparedconventionally in a non-monomeric solvent and advanced to highconversion (degree of polymerization). When solvent (monomeric ornon-monomeric) is used, the solvent may be removed (for example byvacuum distillation) either before or after formation of the syrupcomposition. While an acceptable method, this procedure involving ahighly converted functional polymer is not preferred because anadditional solvent removal step is required, another material may berequired (a non-monomeric solvent), and dissolution of the highmolecular weight, highly converted solute polymer in the monomer mixturemay require a significant period of time.

The polymerization is preferably conducted in the absence of solventssuch as ethyl acetate, toluene and tetrahydrofuran, which arenon-reactive with the functional groups of the components of the syrupcomposition. Solvents influence the rate of incorporation of differentmonomers in the polymer chain and generally lead to lower molecularweights as the polymers gel or precipitate from solution. Thus, the(e.g. pressure sensitive) adhesive can be free of unpolymerizableorganic solvent.

Useful photoinitiators include benzoin ethers such as benzoin methylether and benzoin isopropyl ether; substituted acetophenones such as2,2-dimethoxy-2-phenylacetophenone photoinitiator, available the tradename IRGACURE 651 or ESACURE KB-1 photoinitiator (Sartomer Co., WestChester, Pa.), and dimethylhydroxyacetophenone; substituted α-ketolssuch as 2-methyl-2-hydroxy propiophenone; aromatic sulfonyl chloridessuch as 2-naphthalene-sulfonyl chloride; and photoactive oximes such as1-phenyl-1,2-propanedione-2-(O-ethoxy-carbonyl)oxime. Particularlypreferred among these are the substituted acetophenones.

Preferred photoinitiators are photoactive compounds that undergo aNorrish I cleavage to generate free radicals that can initiate byaddition to the acrylic double bonds. The photoinitiator can be added tothe mixture to be coated after the polymer has been formed, i.e.,photoinitiator can be added to the syrup composition. Such polymerizablephotoinitiators are described, for example, in U.S. Pat. Nos. 5,902,836and 5,506,279 (Gaddam et al.).

Such photoinitiators preferably are present in an amount of from 0.1 to1.0 part by weight, relative to 100 parts by weight of the total syrupcontent. Accordingly, relatively thick coatings can be achieved when theextinction coefficient of the photoinitiator is low.

The syrup composition and the photoinitiator may be irradiated withactivating UV radiation to polymerize the monomer component(s). UV lightsources can be of two types: 1) relatively low light intensity sourcessuch as blacklights, which provide generally 10 mW/cm² or less (asmeasured in accordance with procedures approved by the United StatesNational Institute of Standards and Technology as, for example, with aUVIMAP UM 365 L-S radiometer manufactured by Electronic Instrumentation& Technology, Inc., in Sterling, Va.) over a wavelength range of 280 to400 nanometers; and 2) relatively high light intensity sources such asmedium pressure mercury lamps which provide intensities generallygreater than 10 mW/cm², preferably 15 to 450 mW/cm². Where actinicradiation is used to fully or partially polymerize the syrupcomposition, high intensities and short exposure times are preferred.For example, an intensity of 600 mW/cm² and an exposure time of about 1second may be used successfully. Intensities can range from 0.1 to 150mW/cm², preferably from 0.5 to 100 mW/cm², and more preferably from 0.5to 50 mW/cm².

The degree of conversion can be monitored during the irradiation bymeasuring the index of refraction of the polymerizing medium aspreviously described. Useful coating viscosities are achieved withconversions (i.e., the percentage of available monomer polymerized) inthe range of up to 30%, preferably 2% to 20%, more preferably from 5% to15%, and most preferably from 7% to 12%. The molecular weight (weightaverage) of the solute polymer(s) is typically at least 100,000 or250,000 and preferably at least 500,000 g/mole or greater.

When preparing (meth)acrylic polymers described herein, it is expedientfor the photoinitiated polymerization reactions to proceed to virtualcompletion, i.e., depletion of the monomeric components, at temperaturesless than 70° C. (preferably at 50° C. or less) with reaction times lessthan 24 hours, preferably less than 12 hours, and more preferably lessthan 6 hours. These temperature ranges and reaction rates obviate theneed for free radical polymerization inhibitors, which are often addedto acrylic systems to stabilize against undesired, prematurepolymerization and gelation. Furthermore, the addition of inhibitorsadds extraneous material that will remain with the system and inhibitthe desired polymerization of the syrup composition and formation of thecrosslinked pressure-sensitive adhesives. Free radical polymerizationinhibitors are often required at processing temperatures of 70° C. andhigher for reaction periods of more than 6 to 10 hours.

The pressure-sensitive adhesives may optionally contain one or moreconventional additives. Preferred additives include tackifiers,plasticizers, dyes, antioxidants, UV stabilizers, and (e.g. inorganic)fillers such as (e.g. fumed) silica and glass bubbles.

In some embodiments, the pressure sensitive adhesive comprises fumedsilica. Fumed silica, also known as pyrogenic silica, is made from flamepyrolysis of silicon tetrachloride or from quartz sand vaporized in a3000° C. electric arc. Fumed silica consists of microscopic droplets ofamorphous silica fused into (e.g. branched) three-dimensional primaryparticles that aggregate into larger particles. Since the aggregates donot typically break down, the average particle size of fumed silica isthe average particle size of the aggregates. Fumed silica iscommercially available from various global producers including Evonik,under the trade designation “Aerosil”; Cabot under the trade designation“Cab-O—Sil”, and Wacker Chemie-Dow Corning. The BET surface area ofsuitable fumed silica is typically at least 50 m²/g, or 75 m²/g, or 100m²/g. In some embodiments, the BET surface area of the fumed silica isno greater than 400 m²/g, or 350 m²/g, or 300 m²/g, or 275 m²/g, or 250m²/g. The fumed silica aggregates preferably comprise silica having aprimary particle size no greater than 20 nm or 15 nm. The aggregateparticle size is substantially larger than the primary particle size andis typically at least 100 nm or greater.

The concentration of (e.g. fumed) silica can vary. In some embodiments,such as for conformable pressure sensitive adhesives, the adhesivecomprises at least 0.5, 1. 0, 1.1, 1.2, 1.3, 1.4, or 1.5 wt-% of (e.g.fumed) silica and in some embodiments no greater than 5, 4, 3, or 2wt-%. In other embodiments, the adhesive comprises at least 5, 6, 7, 8,9, or 10 wt-% of (e.g. fumed) silica and typically no greater than 20,19, 18, 17, 16, or 15 wt-% of (e.g. fumed) silica.

In some embodiments, the pressure sensitive adhesive comprises glassbubbles. Suitable glass bubbles generally have a density ranging fromabout 0.125 to about 0.35 g/cc. In some embodiments, the glass bubbleshave a density less than 0.30, 0.25, or 0.20 g/cc. Glass bubblesgenerally have a distribution of particles sizes. In typicalembodiments, 90% of the glass bubbles have a particle size (by volume)of at least 75 microns and no greater than 115 microns. In someembodiments, 90% of the glass bubbles have a particle size (by volume)of at least 80, 85, 90, or 95 microns. In some embodiments, the glassbubbles have a crush strength of at least 250 psi and no greater than1000, 750, or 500 psi. Glass bubbles are commercially available fromvarious sources including 3M, St. Paul, Minn.

The concentration of glass bubbles can vary. In some embodiments, theadhesive comprises at least 1, 2, 3, 4 or 5 wt-% of glass bubbles andtypically no greater than 20, 15, or 10 wt-% of glass bubbles.

The inclusion of glass bubbles can reduce the density of the adhesive.Another way of reducing the density of the adhesive is by incorporationof air or other gasses into the adhesive composition. For example the(e.g. syrup) adhesive composition can be transferred to a frother asdescribed for examples in U.S. Pat. No. 4,415,615; incorporated hereinby reference. While feeding nitrogen gas into the frother, the frothedsyrup can be delivered to the nip of a roll coater between a pair oftransparent, (e.g. biaxially-oriented polyethylene terephthalate) films.A silicone or fluorochemical surfactant is included in the froathedsyrup. Various surfactants are known including copolymer surfactantsdescribed in U.S. Pat. No. 6,852,781.

In some embodiments no tackifier is used. When tackifiers are used, theconcentration can range from 5 or 10 wt-% to 40, 45, 50, 55, or 60 wt-%of the (e.g. cured) adhesive composition.

Various types of tackifiers include phenol modified terpenes and rosinesters such as glycerol esters of rosin and pentaerythritol esters ofrosin that are available under the trade designations “Nuroz”, “Nutac”(Newport Industries), “Permalyn”, “Staybelite”, “Foral” (Eastman). Alsoavailable are hydrocarbon resin tackifiers that typically come from C5and C9 monomers by products of naphtha cracking and are available underthe trade names “Piccotac”, “Eastotac”, “Regalrez”, “Regalite”(Eastman), “Arkon” (Arakawa), “Norsolene”, “Wingtack” (Cray Valley),“Nevtack”, LX (Neville Chemical Co.), “Hikotac”, “Hikorez” (KolonChemical), “Novares” (Rutgers Nev.), “Quintone” (Zeon), “Escorez”(Exxonmobile Chemical), “Nures”, and “H-Rez” (Newport Industries). Ofthese, glycerol esters of rosin and pentaerythritol esters of rosin,such as available under the trade designations “Nuroz”, “Nutac”, and“Foral” are considered biobased materials.

Depending on the kinds and amount of components, the pressure sensitiveadhesive can be formulated to have a wide variety of properties forvarious end uses.

In one specific embodiment, the adhesive composition and thickness ischosen to provide a synergistic combination of properties. In thisembodiment, the adhesive can be characterized as having any one orcombination of attributes including being conformable, cleanlyremovable, reusable, reactivatible, and exhibiting good adhesion torough surfaces.

Thus, in some embodiments, the PSA is conformable. The conformability ofan adhesive can be characterized using various techniques such asdynamic mechanical analysis (as determined by the test method describedin the examples) that can be utilized to determine that shear lossmodulus (G″), the shear storage modulus (G′), and tan delta, defined asthe ratio of the shear loss modulus (G″) to the shear storage modulus(G′). As used herein “conformable” refers to the (e.g. first) adhesiveexhibiting a tan delta of at least 0.4 or greater at 25° C. and 1 hertz.In some embodiments, the (e.g. first) adhesive has tan delta of at least0.45, 0.50, 0.55, 0.65, or 0.70 at 25° C. and 1 hefts. The tan delta at25° C. and 1 hertz of the (e.g. first) adhesive is typically no greaterthan 0.80 or 1.0. In some embodiments, the tan delta of the (e.g. first)adhesive is no greater than 1.0 at 1 hertz and temperatures of 40° C.,60° C., 80° C., 100° C. and 120° C. In some embodiments, the firstadhesive layer has tan delta of at least 0.4 or greater at 1 hertz andtemperatures of 40° C., 60° C., 80° C., 100° C. and 120° C.

The PSA and adhesive coated articles can exhibit good adhesion to bothsmooth and rough surfaces. Various rough surfaces are known includingfor example textured drywall, such as “knock down” and “orange peel”;cinder block, rough (e.g. Brazilian) tile and textured cement. Smoothsurfaces, such as stainless steel, glass, and polypropylene have anaverage surface roughness (Ra) as can be measured by optical inferometryof less than 100 nanometer; whereas rough surfaces have an averagesurface roughness greater than 1 micron (1000 nanometers), 5 microns, or10 microns.

Surfaces with a roughness in excess of 5 or 10 microns can be measuredwith stylus profilometry. Standard (untextured) drywall has an averagesurface roughness (Ra), of about 10-20 microns and a maximum peak height(Rt using Veeco's Vison software) of 150 to 200 microns. Orange peel andknockdown drywall have an average surface roughness (Ra) greater than20, 25, 30, 35, 40, or 45 microns and a maximum peak height (Rt) greaterthan 200, 250, 300, 350, or 400 microns. Orange peel drywall can have anaverage surface roughness (Ra) of about 50-75 microns and a maximum peakheight (Rt) of 450-650 microns. Knock down drywall can have an averagesurface roughness (Ra) greater than 75, 80, or 85 microns, such asranging from 90-120 microns and a maximum peak height (Rt) of 650-850microns. In typical embodiments, Ra is no greater than 200, 175, or 150microns and Rt is no greater than 1500, 1250, or 1000 microns. Cinderblock and Brazilian tile typically have a similar average surfaceroughness (Ra) as orange peel drywall.

Although many conformable adhesives exhibit good initial adhesion to arough surface, the PSA and articles described herein can exhibit a shear(with a mass of 250 g) to orange peel dry wall of at least 500 minutes.In some embodiments, the PSA and articles can exhibit a shear (with amass of 250 g) to orange peel dry wall of at least 1000, 2000, 3000,4000, 5000, 6000, 7000, 8000, 9000 or 10,000 minutes.

The PSA and adhesive coated articles can be cleanly removable frompaper. By “cleanly removable from paper” it is meant that the paper doesnot tear and the paper does not have any staining or adhesive residueafter removal of the adhesive from the paper when tested (according toTest Method 3 set forth in the examples). The 90° peel values to paper(according to Test Method 3, set forth in the examples) is typically atleast 25 and no greater than 200 or 175 N/dm. In some embodiments, the90° peel value to paper no greater than 50, 45, or 40 N/dm.

The PSA and adhesive coated articles can be reusable. By reusable it ismeant that PSA and/or adhesive coated article can repeatedly be removedand readhered to paper at least 1, 2, 3, 4, or 5 times. In someembodiments, it can be readhered to paper at least 5, 10, 15, or 20times while maintaining at least 80%, 85%, or 90% of the initial peeladhesion (according to the “Reusability” test further described in theexamples).

Further, in some embodiments, the adhesive can be reactivatible, i.e.contaminants can be removed by cleaning the adhesive layer(s) with soapand water, such as by the test methods described in WO 96/31564;incorporated herein by reference.

The adhesives of the present invention may be coated upon a variety offlexible and inflexible backing materials using conventional coatingtechniques to produce adhesive-coated materials. Flexible substrates aredefined herein as any material which is conventionally utilized as atape backing or may be of any other flexible material. Examples include,but are not limited to plastic films such as polypropylene,polyethylene, polyvinyl chloride, polyester (polyethyleneterephthalate), polycarbonate, polymethyl(meth)acrylate (PMMA),cellulose acetate, cellulose triacetate, and ethyl cellulose. Foambackings may be used. In some embodiments, the backing is comprised of abio-based material such as polylactic acid (PLA).

Backings may also be prepared of fabric such as woven fabric formed ofthreads of synthetic or natural materials such as cotton, nylon, rayon,glass, ceramic materials, and the like or nonwoven fabric such as airlaid webs of natural or synthetic fibers or blends of these. The backingmay also be formed of metal, metalized polymer films, or ceramic sheetmaterials may take the form of any article conventionally known to beutilized with pressure-sensitive adhesive compositions such as labels,tapes, signs, covers, marking indicia, and the like.

Backings can be made from plastics (e.g., polypropylene, includingbiaxially oriented polypropylene, vinyl, polyethylene, polyester such aspolyethylene terephthalate), nonwovens (e.g., papers, cloths, nonwovenscrims), metal foils, foams (e.g., polyacrylic, polyethylene,polyurethane, neoprene), and the like. Foams are commercially availablefrom various suppliers such as 3M Co., Voltek, Sekisui, and others. Thefoam may be formed as a coextruded sheet with the adhesive on one orboth sides of the foam, or the adhesive may be laminated to it. When theadhesive is laminated to a foam, it may be desirable to treat thesurface to improve the adhesion of the adhesive to the foam or to any ofthe other types of backings. Such treatments are typically selectedbased on the nature of the materials of the adhesive and of the foam orbacking and include primers and surface modifications (e.g., coronatreatment, surface abrasion). Suitable primers include for example thosedescribed in EP 372756, U.S. Pat. No. 5,534,391, U.S. Pat. No.6,893,731, WO2011/068754, and WO2011/38448.

In some embodiments, the backing material is a transparent film having atransmission of visible light of at least 90 percent. The transparentfilm may further comprise a graphic. In this embodiment, the adhesivemay also be transparent.

The above-described compositions can be coated on a substrate usingconventional coating techniques modified as appropriate to theparticular substrate. For example, these compositions can be applied toa variety of solid substrates by methods such as roller coating, flowcoating, dip coating, spin coating, spray coating knife coating, and diecoating. The composition may also be coated from the melt. These variousmethods of coating allow the compositions to be placed on the substrateat variable thicknesses thus allowing a wider range of use of thecompositions. Coating thicknesses may vary as previously described. Thesyrup composition may be of any desirable concentration for subsequentcoating, but is typically 5 to 20 wt-% polymer solids in monomer. Thedesired concentration may be achieved by further dilution of the coatingcomposition, or by partial drying. Coating thicknesses may vary fromabout 25 to 1500 microns (dry thickness). In typical embodiments, thecoating thickness ranges from about 50 to 250 microns. When themultilayer PSA or article is intended to be bonded to a rough surface,the thickness of the adhesive layer typically ranges from the averageroughness (Ra) to slightly greater than the maximum peak height (Rt).

The adhesive can also be provided in the form of a pressure-sensitiveadhesive transfer tape in which at least one layer of the adhesive isdisposed on a release liner for application to a permanent substrate ata later time. The adhesive can also be provided as a single coated ordouble coated tape in which the adhesive is disposed on a permanentbacking.

For a single-sided tape, the side of the backing surface opposite thatwhere the adhesive is disposed is typically coated with a suitablerelease material. Release materials are known and include materials suchas, for example, silicone, polyethylene, polycarbamate, polyacrylics,and the like. For double coated tapes, another layer of adhesive isdisposed on the backing surface opposite that where the adhesive of theinvention is disposed. The other layer of adhesive can be different fromthe adhesive of the invention, e.g., a conventional acrylic PSA, or itcan be the same adhesive as the invention, with the same or a differentformulation. Double coated tapes are typically carried on a releaseliner. Additional tape constructions include those described in U.S.Pat. No. 5,602,221 (Bennett et al.), incorporated herein by reference.

In some embodiments, the pressure sensitive adhesive and a release layerin the release liner are both UV curable compositions. Any conventionalcoating technique can be used to “wet cast” and UV cure the pressuresensitive adhesive directly onto the UV cured release layer of therelease liner. Optionally the UV cured pressure sensitive adhesive is“dry laminated” to the LTV cured release layer of the release liner.

It is desirable to provide tight side release values of 20 grams/inch ormore. It is also desirable to provide a release ratio (tight sideadhesion strength/easy side adhesion release strength) of 3 or more. Arelease ratio of 3 or more contributes to the desired release behaviorwherein the adhesive consistently releases first from the easy side ofthe liner then subsequently from the tight side of the liner. It isfurther desirable to provide both such characteristics simultaneously.

Release materials, such as those useful in the presently disclosedrelease liners, include UV curable compositions made using techniquesdisclosed in US 2013/0059105 (Wright), which is hereby incorporated byreference. In some embodiments, the present disclosure describes amethod for producing a release liner from an at least partially curedlayer (optionally a fully cured layer), the method including applying alayer comprising a (meth)acrylate-functional siloxane to a surface of asubstrate, and irradiating the layer in a substantially inert atmospherewith a short wavelength polychromatic ultraviolet light source having apeak intensity at a wavelength of from about 160 (+/−5) nanometers (nm)to about 240 (+/−5) nm to at least partially cure the layer. Optionally,the layer is at a curing temperature greater than 25° C.

Thus, in some exemplary embodiments, the material comprising the layermay be heated to a temperature greater than 25° C. during or subsequentto application of the layer to the substrate. Alternatively, thematerial comprising the layer may be provided at a temperature ofgreater than 25° C., e.g. by heating or cooling the material comprisingthe layer before, during, and/or after application of the layer to thesubstrate. Preferably, the layer is at a temperature of at least 50° C.,60° C. 70° C., 80° C., 90° C., 100° C., 125° C., or even 150° C.Preferably the layer is at a temperature of no more than 250° C., 225°C., 200° C., 190° C., 180° C., 170° C., 160° C., or even 155° C.

Methods of the present disclosure involve applying a layer comprising a(meth)acrylate-functional siloxane to a major surface of a substrate.Generally, the materials comprising the layer may be oils, fluids, gums,elastomers, or resins, e.g., friable solid resins. Generally, lowermolecular weight, lower viscosity materials are referred to as fluids oroils, while higher molecular weight, higher viscosity materials arereferred to as gums; however, there is no sharp distinction betweenthese terms. Elastomers and resins have even higher molecular weightsthan gums and typically do not flow. As used herein, the terms “fluid”and “oil” refer to materials having a dynamic viscosity at 25° C. of nogreater than 1,000,000 mPa·sec (e.g., less than 600,000 mPa·sec), whilematerials having a dynamic viscosity at 25° C. of greater than 1,000,000mPa·sec (e.g., at least 10,000,000 mPa·sec) are referred to as “gums.”

In order to obtain the low thicknesses generally desirable for somesilicone coatings, e.g., silicone release materials, it is oftennecessary to dilute high molecular weight materials with solvents inorder to coat or otherwise apply them to a substrate. In someembodiments, it may be preferable to use low molecular weight siliconeoils or fluids, including those having a dynamic viscosity at 25° C. ofno greater than 200,000 mPa·sec, no greater than 100,000 mPa·sec, oreven no greater than 50,000 mPa·sec.

In some embodiments, it may be useful to use materials compatible withcommon solventless coating operations, including, e.g., those having akinematic viscosity at 25° C. of no greater than 50,000 centistokes(cSt), e.g., no greater than 40,000 cSt, or even no greater than 20,000cSt. In some embodiments, it may be desirable to use a combination ofsilicone materials, wherein at least one of the silicone materials has akinematic viscosity at 25° C. of at least 5,000 centistokes (cSt), e.g.,at least 10,000 cSt, or even at least 15,000 cSt. In some embodiments,it may be desirable to use materials in the layer having a kinematicviscosity at 25° C. of between 1000 and 50,000 cSt, e.g., between 5,000and 50,000 cSt, or even between 10,000 and 50,000 cSt.

In general, depending on the selected material comprising the layer,including its viscosity, any known coating method may be used. Exemplarycoating methods include roll coating, spray coating, dip coating,gravure coating, bar coating, vapor coating, and the like. Once coated,the silicone material is exposed to short wavelength ultravioletradiation.

In accordance with the method of the disclosure, the(meth)acrylate-functional siloxane may be coated via any of a variety ofconventional coating methods, such as roll coating, knife coating, orcurtain coating. The low viscosity (co)polymerization mixtures arepreferably coated by means specifically adapted to deliver thin releaselayers, preferably through the use of precision roll coaters andelectrospray methods such as those described in U.S. Pat. Nos. 4,748,043and 5,326,598 (both to Seaver et al.). Higher viscosity mixtures whichcan be coated to higher thickness (e.g., up to about 500 μm) can beprovided by selecting higher molecular weight oligomeric startingmaterials. Oligomeric or (co)polymeric starting materials can also bethickened with adjuvants (e.g. thickeners), including but not limited toparticulate fillers such as colloidal silica and the like, prior tocoating.

In some exemplary embodiments of any of the foregoing, the layer isapplied at a thickness of about 0.1 (+/−0.05) micrometer (μm) to about 5(+/−0.1) μm prior to irradiation with the short wavelength polychromaticlight source. In certain exemplary embodiments, the layer is applied ata thickness of at least about 0.2 (+/−0.05) μm, 0.3 (+/−0.05) μm, 0.4(+/−0.05) μm, or even 0.5 (+/−0.05) μm; to about 4 (+/−0.1) μm, 3(+/−0.1) μm, 2 (+/−0.1) μm, or even 1 (+/−0.1) μm, prior to irradiationwith the short wavelength polychromatic light source.

In other exemplary embodiments, the at least partially cured layer oreven the fully cured layer may have a thickness of 0.1 (+/−0.05)micrometer (μm) to about 5 (+/−0.1) μm. In certain exemplaryembodiments, the at least partially cured layer or even the fully curedlayer has a thickness of at least about 0.2 (+/−0.05) μm, 0.3 (+/−0.05)μm, 0.4 (+/−0.05) μm, or even 0.5 (+/−0.05) μm; to about 4 (+/−0.1) μm,3 (+/−0.1) μm, 2 (+/−0.1) μm, or even 1 (+/−0.1) μm.

In any of the foregoing exemplary embodiments, applying the layer to thesurface of the substrate includes applying a discontinuous coating. Inother words, the layer need not cover the entire major surface of thesubstrate, and only a portion of the substrate surface may be covered bythe layer. For example, the layer may be applied to the substrate as asingle strip or stripe, or as a plurality of strips or stripes, as aplurality of dots, or in any other discernible pattern.

Exemplary methods of the present disclosure include UV-radiation curingof the layer, by irradiating the layer, in a substantially inertatmosphere containing no greater than 500 ppm oxygen, with radiation(e.g. light) emitted from a short wavelength polychromatic ultravioletlight source having a peak intensity at a wavelength of from about 160(+/−5) nanometers (nm) to about 240 (+/−5) nm, to at least partiallycure the layer.

Substantially inert atmospheres are particularly useful in embodimentsin which the UV-radiation source has radiant output at wavelengths ofless than 200 nm. In such embodiments, oxygen gas present in theenvironment may absorb the UV radiation, thereby substantiallypreventing the radiation from reaching the target surface. Thus, in anyof the foregoing exemplary embodiments, the substantially inertatmosphere includes no greater than 500 ppm oxygen. In some of theforegoing exemplary embodiments, the substantially inert atmosphereincludes no greater than 400 ppm oxygen, 300 ppm oxygen, 200 ppm oxygen,or even 100 ppm oxygen. In some of the foregoing exemplary embodiments,the substantially inert atmosphere includes no greater than 50 ppmoxygen, no greater than 40 ppm, 30 ppm, 20 ppm, or even 10 ppm oxygen.

In some exemplary embodiments, the substantially inert atmosphere maycomprise an inert gas such as nitrogen, helium, argon, or the like. Inone embodiment, the methods of the present disclosure may be carried outin an inert environment including nitrogen. In embodiments in which aninert gas is used, oxygen levels in the environment may be as low as 50ppm, 25 ppm, or even as low as 10 ppm, and as high as 100 ppm, or even500 ppm.

In further exemplary embodiments, the controlled environment may beoperated in a vacuum or a partial vacuum. In some such embodiments inwhich vacuum pressures are employed, the pressures may be as low as 10⁻⁴torr, 10⁻⁵ torr, or even as low as 10⁻⁶ torr; and be as high as 10⁻¹torr, 1 torr, or even 10 torr.

In further exemplary embodiments, the material comprising the layer isexposed to short wavelength polychromatic ultraviolet radiation afterapplying the layer to the substrate, to at least partially cure thelayer on the substrate. Short wavelength polychromatic ultraviolet lightsources useful in the method of the present disclosure are those havingoutput in the region from about 160 (+/−5) nm to about 240 (+/−5) nm,inclusive. In some exemplary embodiments of any of the foregoing, a peakintensity is at a wavelength between about 170 (+/−5) nm, 180 (+/−5) nm,or even 190 (+/−5) nm; to about 215 (+/−5) nm, 210 (+/−5) nm, 205 (+/−5)nm, or even 200 (+/−5) nm. In some particular exemplary embodiments, apeak intensity is at a wavelength of about 185 (+/−2) nm.

In certain such exemplary embodiments, the short wavelengthpolychromatic ultraviolet light source includes at least one lowpressure mercury vapor lamp, at least one low pressure mercury amalgamlamp, at least one pulsed Xenon lamp, at least one glow discharge from apolychromatic plasma emission source, or combinations thereof.

Suitable plasma emission sources may involve excitation of a carrier gas(e.g. nitrogen) to generate electrons, ions, radicals, and photons inthe form of a glow discharge. As reported in, for example, Elsner et al.[Macromol. Mater. Eng., 294, 422-31 (2009)], a variety of acrylatemonomers can be cured in the absence of photoinitiators using a nitrogenplasma polymerization process in which a glow discharge (i.e.,UV-radiation emission) having peak intensities near 150 nm, 175 nm, and220 nm was observed.

The intensities of incident radiation useful in the processes of thepresent disclosure can be from as low as about 1 mW/cm² to about 10W/cm², preferably 5 mW/cm² to about 5 W/cm², more preferably 10 mW/cm²to 1 W/cm². When higher power levels are provided (e.g., greater thanabout 10 W/cm²), volatilization of low molecular weight(meth)acrylate-functional siloxane monomers and oligomers can result.

In some exemplary embodiments, it is desirable to select a shortwavelength polychromatic ultraviolet source having an intensity peak ata wavelength resulting in an absorbance greater than zero but no greaterthan about 0.5 (+/−0.05), as determined by Beer's law for the particularsilicone resin being cured and the thickness. When the absorbance goesabove 0.5, a surface layer or skin may form due to the lack ofpenetration of the radiation through the coating thickness resulting insurface absorption and localized polymerization and cross-linking.Absorbances below 0.3 are acceptable and tend to give more uniformpenetration and cure profiles but are less efficient in terms ofradiation capture.

In certain exemplary embodiments, the absorbance determined by Beer'slaw is between 0.3 and 0.5, inclusive, e.g., between 0.4 and 0.5,inclusive, or even between 0.40 and 0.45, inclusive. As the actualabsorbance and the absorbance calculated by Beer's law increase linearlywith thickness, a particular silicone resin may have the desiredabsorbance at one thickness, e.g., 1 micrometer, while the absorbance ofthe same silicone resin at a greater thickness, e.g., 10 micrometers,may be too high.

The layer comprises material that is capable of undergoing at least apartial cure when exposed to short wavelength polychromatic ultravioletradiation. In the presently disclosed embodiments, the layer comprisesat least one (meth)acrylate-functional siloxane. In some such exemplaryembodiments of any of the foregoing disclosed embodiments, the releaseliner layer consists essentially of one or more(meth)acrylate-functional siloxane monomers. In other such exemplaryembodiments, the layer consists essentially of one or more(meth)acrylate-functional siloxane oligomers. In certain other suchexemplary embodiments, the layer consists essentially of one or more(meth)acrylate-functional polysiloxanes.

The curable materials are applied as a layer on at least a portion of atleast one major surface of a suitable flexible or rigid substrate orsurface or backing, and irradiated using the prescribed ultravioletradiation sources. Useful flexible substrates include, but are notlimited to, paper, poly-coated Kraft paper, supercalendered or glassineKraft paper, plastic films such as poly(propylene), biaxially-orientedpolypropylene, poly(ethylene), poly(vinyl chloride), polycarbonate,poly(tetrafluoroethylene), polyester [e.g., poly(ethyleneterephthalate)], poly(ethylene naphthalate), polyamide film such asthose commercially available under the trade designation “KAPTON” fromDuPont, Wilmington, Del., cellulose acetate, and ethyl cellulose.

In addition, suitable substrates for use in the presently disclosedrelease liner may be formed of metal, metal foil, metallized(co)polymeric film, or ceramic sheet material. Substrates may also takethe form of a cloth backing, e.g. a woven fabric formed of threads ofsynthetic fibers, or a nonwoven web or substrate, or combinations ofthese. One of the advantages of the use of the short wavelengthpolychromatic ultraviolet light sources of the present disclosure is theability to use such high energy, low heat sources to (co)polymerizemixtures coated on heat sensitive substrates. Commonly used longerwavelength ultraviolet lamps often generate undesirable levels ofthermal radiation that can distort or damage a variety of synthetic ornatural flexible substrates. Suitable rigid substrates include but arenot limited to glass, wood, metals, treated metals (such as thosecomprising automobile and marine surfaces), (co)polymeric material andsurfaces, and composite material such as fiber reinforced plastics.

In some exemplary embodiments, the substrates may be surface treated(e.g., corona or flame treatment), coated with, e.g., a primer or printreceptive layer. In certain exemplary embodiments, multilayer substratesmay be used. In certain exemplary embodiments, the substrate may besmooth or textured, e.g., embossed. In some exemplary embodiments, thesubstrate is embossed after curing the release material.

In general, (co)polymerizable (meth)acrylate-functional siloxanes areuseful materials for preparing an at least partially (or in someembodiments completely) cured layer for a layer according to the presentdisclosure. Ethylenically unsaturated free radically (co)polymerizablesiloxanes, including especially the (meth)acrylate-functional siloxaneoligomers and (co)polymers containing telechelic and/or pendant acrylateor methacrylate groups, are particularly useful precursor materials forincorporation in the at least partially cured layers of the presentdisclosure. These (meth)acrylate-functional siloxane oligomers can beprepared by a variety of methods, generally through the reaction ofchloro-, silanol-, aminoalkyl-, epoxyalkyl-, hydroxyalkyl-, vinyl-, orsilicon hydride-functional polysiloxanes with a corresponding(meth)acrylate-functional capping agent. These preparations are reviewedin a chapter entitled “Photo(co)polymerizable Silicone Monomers,Oligomers, and Resins” by A. F. Jacobine and S. T. Nakos in RadiationCuring Science and Technology, (Plenum: New York, 1992), pp. 200-214.

Suitable (co)polymerizable (meth)acrylate-functional siloxane oligomersinclude those (meth)acryl-modified polylsiloxane resins commerciallyavailable from, for example, Goldschmidt Chemical Corporation (EvonikTEGO Chemie GmbH, Essen, Germany) under the TEGO™ RC designation. Anexample of a blend recommended for achieving premium (easy) release is a70:30 (weight/weight, w/w) blend of TEGO RC922 and TEGO RC711.

Suitable (meth)acrylate-functional polysiloxane resins include theacrylamido-terminated monofunctional and difunctional polysiloxaneresins described in U.S. Pat. No. 5,091,483 (Mazurek et al.). These(meth)acrylate-functional polysiloxane resins are pourable and may beblended for optimized properties such as level of release, adhesivecompatibility, and substrate adhesion.

In some exemplary embodiments, the (co)polymerizable precursorcomposition making up the layer may include essentially only one or more(co)polymerizable (meth)acrylate-functional siloxane(s), and issubstantially-free of other (co)polymerizable materials. Thus, infurther exemplary embodiments of any of the foregoing, the layerconsists essentially of one or more (meth)acrylate-functional siloxanemonomers. In some such exemplary embodiments, the layer consistsessentially of one or more (meth)acrylate-functional siloxane oligomers.In other such exemplary embodiments, the layer consists essentially ofone or more (meth)acrylate-functional polysiloxanes.

In addition to the (meth)acrylate functional siloxane, the layer mayoptionally include one or more (co)polymerizable starting materials.Suitable (co)polymerizable starting materials may contain silicon or maynot contain silicon.

Thus, in some exemplary embodiments, the layer further comprises anon-(meth)acrylate-functional siloxane monomer, oligomer, or(co)polymer. Such materials can be functional or non-functional.Examples of non-functional (co)polymerizable siloxanes includepoly(dialkylsiloxanes), poly(dialkyldiarylsiloxanes),poly(alkylarylsiloxanes), and poly(diarylsiloxanes), and may be linear,cyclic, or branched. Examples of functional (butnon-(meth)acrylate-functional) polysiloxanes that may be used includevinyl-functional polysiloxanes, hydroxy-functional polysiloxanes,amine-functional polysiloxanes, hydride-functional polysiloxanes,epoxy-functional polysiloxanes, and combinations thereof.

In certain exemplary embodiments, the layer further comprises one ormore (co)polymerizable materials selected from the group consisting ofmonofunctional (meth)acrylate monomers, difunctional (meth)acrylatemonomers, polyfunctional (meth)acrylate monomers having functionalitygreater than two, vinyl ester monomers, vinyl ester oligomers, vinylether monomers, and vinyl ether oligomers. Suitable vinyl-functionalmonomers include but are not limited to acrylic acid and its esters,methacrylic acid and its esters, vinyl-substituted aromatics,vinyl-substituted heterocyclics, vinyl esters, vinyl chloride,acrylonitrile, methacrylonitrile, acrylamide and derivatives thereof,methacrylamide and derivatives thereof, and other vinyl monomers(co)polymerizable by free-radical means.

Monofunctional (meth)acrylate (co)monomers useful in the methods of thepresent disclosure include compositions of Formula 1:

[X—]_(m)—Z  (1)

wherein X represents H₂C═C(R₁)C(O)O—, in which R₁ represents —H or —CH₃,m=1, and Z represents a monovalent straight chain alkyl, branched alkylor cycloalkyl group having from about 1 to about 24 carbon atoms. Aclass of particularly suitable monofunctional (co)monomers includemonoethylenically unsaturated monomers having homopolymer glasstransition temperatures (T_(g)) greater than about 0° C., preferablygreater than 15° C.

Examples of suitable monofunctional (meth)acrylate monomers include butare not limited to those selected from the group consisting ofmethyl(meth)acrylate, isooctyl(meth)acrylate,4-methyl-2-pentyl(meth)acrylate, 2-methylbutyl(meth)acrylate,isoamyl(meth)acrylate, sec-butyl(meth)acrylate, n-butyl(meth)acrylate,tert-butyl(meth)acrylate, isobornyl(meth)acrylate, butyl methacrylate,ethyl(meth)acrylate, dodecyl(meth)acrylate, octadecyl(meth)acrylate,cyclohexyl(meth)acrylate and mixtures thereof.

Particularly suitable monofunctional (meth)acrylate monomers includethose selected from the group consisting of isooctyl(meth)acrylate,isononyl(meth)acrylate, isoamyl(meth)acrylate, isodecyl(meth)acrylate,2-ethylhexyl(meth)acrylate, isobornyl(meth)acrylate,n-butyl(meth)acrylate, sec-butyl(meth)acrylate, and mixtures thereof.

Monofunctional vinyl ester monomers useful in the methods of the presentdisclosure include compositions of Formula 1 wherein X representsH₂C═CHOC(O)—, m=1, and Z represents a monovalent straight chain orbranched alkyl group having from about 1 to about 24 atoms. Such vinylester monomers include but are not limited to those selected from thegroup consisting of vinyl acetate, vinyl 2-ethylhexanoate, vinylcaprate, vinyl laureate, vinyl pelargonate, vinyl hexanoate, vinylpropionate, vinyl decanoate, vinyl octanoate, and other monofunctionalunsaturated vinyl esters of linear or branched carboxylic acidscomprising 1 to 16 carbon atoms. Preferred vinyl ester monomers includethose selected from the group consisting of vinyl acetate, vinyllaureate, vinyl caprate, vinyl-2-ethylhexanoate, and mixtures thereof.

Other suitable monofunctional (co)monomers include but are not limitedto those selected from the group consisting of acrylic acid, methacrylicacid, itaconic acid, crotonic acid, maleic acid, fumaric acid,sulfoethyl methacrylate, N-vinyl pyrrolidone, N-vinyl caprolactam,acrylamide, t-butyl acrylamide, dimethyl amino ethyl acrylamide, N-octylacrylamide, acrylonitrile, mixtures thereof, and the like. Preferredmonomers include those selected from the group consisting of acrylicacid, N-vinyl pyrrolidone, and mixtures thereof.

Free radically (co)polymerizable monofunctional macromonomers oroligomers (i.e., macromers) of Formula 1, wherein X is H₂C═CR₁COO—, R₁represents —H or —CH₃, m is 1, and Z is a monovalent (co)polymeric oroligomeric radical having a degree of (co)polymerization greater than orequal to 2, and that are substantially free of aromatic, chloro- andother moieties or substituents that significantly absorb ultravioletradiation in the range of about 160 nm to about 240 nm, may also be usedin the at least partially cured layers of the present disclosure.

Examples of such monofunctional macromonomers or oligomers include thoseselected from the group consisting of (meth)acrylate-terminatedpoly(methyl methacrylate), methacrylate-terminated poly(methylmethacrylate), (meth)acrylate-terminated poly(ethylene oxide),methacrylate-terminated poly(ethylene oxide), (meth)acrylate-terminatedpoly(ethylene glycol), methacrylate-terminated poly(ethylene glycol),methoxy poly(ethylene glycol) methacrylate, butoxy poly(ethylene glycol)methacrylate, and mixtures thereof. These functionalized materials arepreferred because they are easily prepared using well-known ionic(co)polymerization techniques and are also highly effective in providinggrafted oligomeric and (co)polymeric segments along free radically(co)polymerized (meth)acrylate (co)polymer backbones.

The viscosity of such monofunctional macromonomers or oligomers usefulin practicing the methods of the present disclosure are generally highenough so that a thickener is not usually necessary; however; ifdesired, a thickener or particulate filler may be advantageously used asan adjuvant, as described further below.

Useful difunctional and other polyfunctional (meth)acrylate-functionalfree radically (co)polymerizable monomers include ester derivatives ofalkyl diols, triols, tetrols, etc. (e.g., 1,4-butanedioldi(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropanetri(meth)acrylate, and pentaerythritol tri(meth)acrylate). Difunctionaland polyfunctional (meth)acrylate and methacrylate monomers described inU.S. Pat. No. 4,379,201 (Heilmann et al.), such as 1,2-ethanedioldi(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, pentaerythritoltetr(meth)acrylate can also be used in the present disclosure.

Difunctional and polyfunctional (meth)acrylates and methacrylatesincluding (meth)acrylated epoxy oligomers, (meth)acrylated aliphaticurethane oligomers, (meth)acrylated polyether oligomers, and(meth)acrylated polyester oligomers, such as those commerciallyavailable from UCB Radcure Inc, Smyrna, Ga. under the EBECRYL tradename,and those available from Sartomer, Exton, Pa., may also be employed.

In further exemplary embodiments, the layer further includes at leastone non-functional polysiloxane material. In some such further exemplaryembodiments, the at least one non-functional polysiloxane material isselected from a poly(dialkylsiloxane), a poly(alkylarylsiloxane), apoly(diarylsiloxane), or a poly(dialkyldiarylsiloxane), optionallywherein the non-functional polysiloxane material comprises from 0.1 to95 wt. %, inclusive, of the layer.

The non-functional polysiloxane material can be described generally bythe following formula illustrating a siloxane backbone with a variety ofsubstituents:

R1 through R4 represent the substituents pendant from the siloxanebackbone. Each R5 may be independently selected and represent theterminal groups. Subscripts n and m are independently integers, and atleast one of m or n is not zero.

As used herein, a “nonfunctional polysiloxane material” is one in whichthe R1, R2, R3, R4, and R5 groups are nonfunctional groups. As usedherein, “nonfunctional groups” are either alkyl or aryl groupsconsisting of carbon, hydrogen, and in some embodiments, halogen (e.g.,fluorine) atoms. In some embodiments, R1, R2, R3, and R4 areindependently selected from the group consisting of an alkyl group andan aryl group, and R5 is an alkyl group. In some embodiments, one ormore of the alkyl or aryl groups may contain a halogen substituent,e.g., fluorine. For example, in some embodiments, one or more of thealkyl groups may be —CH₂CH₂C₄F₉.

In certain exemplary embodiments, R5 is a methyl group, i.e., thenonfunctional polysiloxane material is terminated by trimethylsiloxygroups. In some embodiments, R1 and R2 are alkyl groups and n is zero,i.e., the material is a poly(dialkylsiloxane). In certain embodiments,the alkyl group is a methyl group, i.e., poly(dimethylsiloxane)(“PDMS”). In other embodiments, R1 is an alkyl group, R2 is an arylgroup, and n is zero, i.e., the material is a poly(alkylarylsiloxane).In some particular embodiments, R1 is a methyl group and R2 is a phenylgroup, i.e., the material is poly(methylphenylsiloxane). In otherparticular embodiments, R1 and R2 are alkyl groups and R3 and R4 arearyl groups, i.e., the material is a poly(dialkyldiarylsiloxane). Incertain additional embodiments, R1 and R2 are methyl groups, and R3 andR4 are phenyl groups, i.e., the material ispoly(dimethyldiphenylsiloxane).

In further exemplary embodiments, the polysiloxane backbone may belinear. In some alternative exemplary embodiments, the polysiloxanebackbone may be branched. For example, one or more of the R1, R2, R3,and/or R4 groups may be a linear or branched siloxane with functional ornonfunctional (e.g., alkyl or aryl, including halogenated alkyl or aryl)pendant and terminal groups. In other alternative exemplary embodiments,the polysiloxane backbone may be cyclic. For example, the siliconematerial may be octamethylcyclotetrasiloxane,decamethylcyclo-pentasiloxane, or dodecamethylcyclohexasiloxane.

In addition to the foregoing polysiloxanes, various(polyalkyl)disiloxanes may be advantageously used in the release linerlayer in addition to or in place of at least a portion of thenon-functional polysiloxane material. In some exemplary embodiments,hexamethyldisiloxane (i.e. O[Si(CH₃)₃]₂) may be used advantageously assuch a non-functional (polyalkyl)disiloxane.

In some exemplary embodiments, the polysiloxane material may befunctional. Generally, functional silicone systems include specificreactive groups attached to the linear, branched, or polysiloxanebackbone of the starting material. For example, a linear “functionalpolysiloxane material” is one in which at least one of the R-groups ofFormula 3 is a functional group:

In some such embodiments, a functional polysiloxane material is one inwhich at least 2 of the R-groups are functional groups. Generally, theR-groups of Formula 3 may be independently selected. In someembodiments, all functional groups are hydroxy groups and/or alkoxygroups. In certain such exemplary embodiments, the functionalpolysiloxane is a silanol terminated polysiloxane, e.g., a silanolterminated poly(dimethylsiloxane). In other such embodiments, thefunctional silicone is an alkoxy terminated poly(dimethylsiloxane),e.g., trimethylsiloxy terminated poly(dimethylsiloxane).

Other functional groups include those having an unsaturatedcarbon-carbon bond such as alkene-containing groups (e.g., vinyl groupsand allyl groups) and alkyne-containing groups.

In addition to at least one functional R-group, the remaining R-groupsmay be nonfunctional groups, e.g., alkyl or aryl groups, includinghalogenated (e.g., fluorinated) alky and aryl groups. In someembodiments, the functionalized polysiloxane materials may be branched.For example, one or more of the R groups may be a linear or branchedsiloxane with functional and/or non-functional substituents. In someembodiments, the functionalized polysiloxane materials may be cyclic.

Although some embodiments of the present disclosure describe the use offunctional silicone materials, the nature of the functional group isgenerally not critical to obtaining the desired cross-linked or curedpolysiloxane materials. Although some reactions may occur through thefunctional groups, direct cross-linking between the polysiloxanebackbones is often sufficient to obtain the desired degree of cure.

Various materials may be advantageously added to the (co)polymerizablecomposition used in forming the release liner layer in order to achieveadvantageous effects. Some such adjuvants include, but are not limitedto, the following optional additives.

In contrast to most previous methods for curing functional materials,the methods of the present disclosure do not require the use of addedcatalysts or initiators (e.g. photoinitiators). Thus, advantageously, insome exemplary embodiments, the methods of the present disclosure do notrequire the use of an added photoinitiator. In other words, exemplarymethods of the present disclosure can be used to cure compositions thatare “substantially free” of such catalysts or initiators (e.g.,photoinitiators).

As used herein, a composition is “substantially free of added catalystsand initiators” if the composition does not include an “effectiveamount” of an added catalyst or initiator. As is well understood, an“effective amount” of a catalyst or initiator depends on a variety offactors including the type of catalyst or initiator, the composition ofthe curable material, and the curing method (e.g., thermal cure,UV-cure, and the like). In some embodiments, a particular catalyst orinitiator is not present at an “effective amount” if the amount ofcatalyst or initiator does not reduce the cure time of the compositionby at least 10% relative to the cure time for the same composition atthe same curing conditions absent that catalyst or initiator.

As stated above, the use of added photoinitiators in the(co)polymerization of (meth)acrylate-functional siloxanes and oligomersintroduces added costs and undesirable residuals and byproducts to theprocess. Articles bearing release layers prepared using the preferredinitiator-free method are of particular significance in medicalapplications, where photoinitiator-induced contamination of releaselayers can lead to skin irritation and other undesirable reactions.Exclusion of this component can result in significant direct costsavings, plus elimination of any expenses involved in qualifyingproducts containing significant amounts of a photoinitiator.

In other exemplary embodiments, an optional added photoinitiator may beadvantageously included in the (co)polymerizable composition.Photoinitiators are particularly useful when higher (co)polymerizationrates or very thin release layers (or surface cures) are required. Whenused, photoinitiators can constitute from as low as about 0.001 to about5 percent by weight of a (co)polymerization mixture. Thesephotoinitiators can be organic, organometallic, or inorganic compounds,but are most commonly organic in nature. Examples of commonly usedorganic photoinitiators include benzoin and its derivatives, benzilketals, acetophenone, acetophenone derivatives, benzophenone, andbenzophenone derivatives.

In contrast to most previous methods for curing functional materials,the methods of the present disclosure do not require the use of organicsolvents. Thus, in any of the foregoing exemplary embodiments, the layermay be (is) substantially free of an organic solvent. In any of theforegoing exemplary embodiments that are substantially free of organicsolvent, the substantially inert atmosphere preferably includes nogreater than 500 ppm oxygen, even more preferably no greater than 50 ppmoxygen.

In additional exemplary embodiments of any of the foregoing, the(co)polymerizable composition may further comprises a thickener. Athickener may be used in the (co)polymerizable composition of thepresent disclosure. A thickener may be used with monomers, but aregenerally not necessary with oligomers. Thickeners can increase theviscosity of the (co)polymerizable composition. The viscosity needs tobe high enough to enable the (co)polymerizable composition to becoatable. In addition, the relatively high viscosity may play a role incontributing to the isolation of the free radicals, thereby improvingconversion and reducing termination. A viscosity in the range of about400-25,000 centipoise is typically desired.

Suitable thickeners are those which are soluble in the (co)polymerizablecomposition, and generally include oligomeric and polymeric materials.Such materials can be selected to contribute various desired propertiesor characteristics to resultant article. Examples of suitable polymericthickening agents include copolymers of ethylene and vinyl esters orethers, poly(alkyl acrylates), poly(alkyl methacrylates), polyesterssuch as poly(ethylene maleate), poly(propylene fumarate), poly(propylenephthalate), and the like.

Other suitable thickeners are particulate fillers which are insoluble inthe (co)polymerizable composition, including but not limited tocolloidal particulates having a median particle diameter of less thanone micrometer. Suitable inorganic colloidal particulate fillers thatmay be used to good advantage as thickeners and/or adjuvants includecommercially available fumed colloidal silicas such as CAB-β-SILs (CabotCorp., Billerica, Mass.) and AER-O-SILs (Evonik North America,Parsippany, N.J.), colloidal alumina, and the like.

An exemplary apparatus for using short wavelength polychromaticultraviolet radiation to cure a coating on a substrate is illustrated byFIG. 2. Exemplary substrates 10 each bearing a layer (e.g., 10A, 10B,10C, 10D) of a UV-curable (co)polymerizable composition may be attachedat various locations on the surface 21 of back up roll 20 located invacuum chamber 30, as illustrated in FIG. 2. Short wavelengthpolychromatic ultraviolet radiation source(s) 40 (e.g., low-pressureshort wavelength polychromatic mercury lamps) may be used to achievecuring of the layers on the substrates, thereby forming an at leastpartially cured layer (optionally a fully cured layer), such as e.g. arelease layer or low adhesion backsize (LAB).

It will be understood that other apparatus, for example a continuousroll-to-roll web coater as described in U.S. Pat. No. 6,224,949, may beused in conjunction with one or more short wavelength polychromaticultraviolet radiation sources to at least partially cure a layer of the(co)polymerizable composition on a substrate, for example, a continuousweb or roll of material (e.g., a (co)polymeric film).

In further exemplary embodiments of any of the foregoing, the at leastpartially cured layer may be a release layer in a UV-radiation curedarticle, such as a liner or an adhesive tape or film. Optionally, theUV-radiation cured release layer is used as a surface release layer in arelease liner, or as a low adhesion backsize (LAB) in an adhesivearticle.

UV-radiation cured layers prepared according to the methods of thepresent disclosure may be used in any of a wide variety of applications,including, e.g., as release layers, low adhesion backsize layers, andthe like. Various exemplary applications are illustrated in FIG. 3.Article 100 comprises first substrate 110 and cross-linked siliconelayer 120 adhered to first surface 111 of first substrate 110 formingrelease liner 210. In some such exemplary embodiments, the release layerhas an unaged peel adhesion less than about 1.6 Newtons per decimeter.Optionally, the release layer has an aged peel adhesion less than 50percent greater than the unaged peel adhesion.

Another particularly useful coating derived from the method of thepresent disclosure involves the (co)polymerization of a (meth)acrylatedsiloxane to form a release layer under a substantially inert (i.e.oxygen content no greater than 500 ppm) atmosphere. The use of siliconerelease layers has been an industry standard for many years, and iswidely employed by liner suppliers and large, integrated tapemanufacturers. Release layers prepared in this manner may exhibit anydesired level of release, including (1) premium or easy release, (2)moderate or controlled release, or (3) tight release; premium releaserequires the least amount of force.

Premium release layers (i.e., those release layers having aged releaseforces in the range of up to about 1.0 N/dm) are typically used inrelease liner applications. Premium release layers are less useful,however, when coated on the back surface of pressure-sensitive adhesivetapes, because their low release force can cause tape roll instabilityand handling problems. Such a release layer on the back surface of apressure-sensitive adhesive tape construction is often referred to as a“low adhesion backsize.” Release layers having moderate to high levelsof aged release (about 4.0 to about 35 N/dm) are especially useful whenused as low adhesion backsizes.

In addition, layers containing (meth)acrylated polysiloxanes for use inthe production of release layers may include, as (co)polymerizableconstituents, 100% (meth)acrylated polysiloxanes or, alternatively mayinclude free radically (co)polymerizable diluents in addition to the(meth)acrylated polysiloxanes. Such non-polysiloxane free radically(co)polymerizable diluents can be used to modify the release propertiesof the release layers of the present disclosure and also enhance thecoating's mechanical properties and anchorage to backings or substratesused in pressure-sensitive adhesive tape or release liner constructions.

Depending on the ultimate properties desired in the (co)polymerizedrelease layers, useful non-polysiloxane free radically (co)polymerizablediluents include monofunctional, difunctional and polyfunctional(meth)acrylate vinyl ether, and vinyl ester monomers and oligomers.Difunctional and polyfunctional (meth)acrylate and methacrylate monomerssuch as 1,4-butanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, trimethylolpropane di(meth)acrylate, pentaerythritoltri(meth)acrylate 1,2-ethanediol di(meth)acrylate, 1,12 dodecanedioldi(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritoltetra(meth)acrylate and difunctional and polyfunctional (meth)acrylateand methacrylate oligomers including (meth)acrylated epoxy oligomers,(meth)acrylated aliphatic urethane oligomers, (meth)acrylated polyesteroligomers, and (meth)acrylated polyethers such as those commerciallyavailable from Cytec Surface Specialties, Woodland Park, N.J. under thetrade designation “EBECRYL”, and from Sartomer, Exton, Pa., may also beadvantageously employed.

The difunctional and polyfunctional (meth)acrylate monomers andoligomers employed in these release layers can be used at aconcentration of from about 5 to about 95 weight percent, preferablyfrom about 10 to 90 weight percent, based on the total weight of therelease layer composition. Monofunctional monomers, such as the(meth)acrylate, vinyl ester and other free radically co(co)polymerizablemonomers listed above, can also be added as non-polysiloxane freeradically (co)polymerizable diluents in the release layer composition.When used, these monofunctional monomers may be employed at aconcentration of up to about 25 weight percent based on the total weightof the release layer composition. Mixtures of monofunctional,difunctional and polyfunctional non-polysiloxane monomers and oligomerscan also be used.

In another aspect, an adhesive article includes the foregoing releaselayer, and an adhesive layer adjacent to the release layer. Optionally,the adhesive layer includes one or more adhesive selected from apressure sensitive adhesive, a hot melt adhesive, a radiation curableadhesive, a tackified adhesive, a non-tackified adhesive, a syntheticrubber adhesive, a natural rubber adhesive, a (meth)acrylic (co)polymeradhesive, and a polyolefin adhesive. In some embodiments, the adhesivemay comprise a pressure sensitive adhesive, which preferably comprises a(meth)acrylic (co)polymer.

Thus, in some exemplary embodiments shown in FIG. 3, in addition torelease liner 210, article 100 further comprises adhesive 140 releasablyadhered to cross-linked silicone layer 120, forming transfer tape 220.In some embodiments, article 100 further comprises second substrate 150adhered to adhesive 140, opposite cross-linked silicone layer 120.

In certain exemplary embodiments, the second substrate may be a releaseliner, e.g., a release liner similar to release liner 210, and article100 may be a dual-linered transfer tape. In some embodiments, the secondsubstrate may be permanently bonded to the adhesive and adhesive article100 may be, for example, a tape or label.

Although not shown, in some embodiments, substrate 110 may be coated onboth sides with a release material. In general, the release materialsmay be independently selected, and may be the same or different releasematerials. In some embodiments, both release materials are preparedaccording to the methods of the present disclosure. In some embodiments,self-wound adhesive articles may be prepared from such two-sided releaseliners. In some embodiments, one or more primer layers may be included.For example, in some embodiments, a primer layer may be located atsurface 111 of substrate 110.

In various embodiments, the rolls of adhesive coated substrates of thepresent disclosure may be rolls of an adhesive tape that includes abacking layer and an adhesive coating disposed on a major surface of thebacking layer. Common types of adhesive tapes include masking tape,electrical tape, duct tape, filament tape, medical tape, transfer tape,and the like.

The adhesive tape rolls may further include a release coating, or lowadhesion backsize, disposed on a second major surface. Alternatively,the adhesive tape rolls may include a release liner (which may have arelease coating disposed on a major surface thereof) in contact with theadhesive coated major surface of the backing layer. As another example,an adhesive tape roll may include a release liner comprising a releasecoating disposed on at least a portion of each of its major surfaces andan adhesive coating deposited over one of the release coatings.

Examples of suitable backing layers include, without limitation,CELLOPHANE, acetate, fiber, polyester, vinyl, polyethylene,polypropylene including, e.g., monoaxially oriented polypropylene andbiaxially oriented polypropylene, polycarbonate,polytetrafluoroethylene, polyvinylfluoroethylene, polyurethane,polyimide, paper (e.g., Kraft paper), woven webs (e.g., cotton,polyester, nylon and glass), nonwoven webs, foil (e.g., aluminum, lead,copper, stainless steel and brass foil tapes) and combinations thereof.

The backing layers and release liners, can also include reinforcingagents including, without limitation, fibers, filaments (e.g., glassfiber filaments), and saturants (e.g., synthetic rubber latex saturatedpaper backings).

Objects and advantages of this invention are further illustrated by thefollowing examples. The particular materials and amounts, as well asother conditions and details, recited in these examples should not beused to unduly limit this invention.

EXAMPLES

As used herein, all percentages and parts are by weight. Amounts ofadditives, e.g., crosslinkers, photoinitiator, tackifiers, etc. areexpressed in parts per hundred resin (phr) in which 100 parts of theresin represents the weight of the monomers that form the polymerbackbone, e.g., IOA, 2OA, AA.

Test Methods Test Method 1: Shear Strength Test 1

Stainless steel (SS) plates were prepared for testing by cleaning withmethyl ethyl ketone and a clean KIMWIPE tissue (Kimberly-ClarkCorporation, Neenah, Wis.) three times. The adhesive films describedwere cut into strips (1.27 cm in width) and adhered by their adhesive toflat, rigid stainless steel plates with exactly 2.54 cm length of eachadhesive film strip in contact with the plate to which it was adhered. Aweight of 2 kilograms (4.4 pounds) was over the adhered portion. Each ofthe resulting plates with the adhered film strip was equilibrated atroom temperature for 15 minutes. Afterwards, the samples weretransferred to a 70° C. oven, in which a 500 g weight was hung from thefree end of the adhered film strip with the panel tilted 2° from thevertical to ensure against any peeling forces. The time (in minutes) atwhich the weight fell, as a result of the adhesive film strip releasingfrom the plate, was recorded. The test was discontinued at 10,000minutes if there was no failure. In the Tables, this is designated as10,000+ minutes. Two specimens of each tape (adhesive film strip) weretested and the shear strength tests were averaged to obtain the reportedshear value in Tables 1-7. In some cases, the samples were prepared andhung in the same fashion but at room temperature (RT) rather than 70° C.The temperature at which the test was carried out is indicated in eachtable.

Test Method 2: 180° Angle Peel Adhesion Test 1

Peel adhesion was the force required to remove an adhesive-coated testspecimen from a test panel measured at a specific angle and rate ofremoval. In the Examples, this force is expressed in ounces per inchwidth of coated sheet and the results are normalized to N/dm. Thefollowing procedure was used:

Peel adhesion strength was measured at a 180° peel angle using an IMASSSP-200 slip/peel tester (available from IMASS, Inc., Accord Mass.) at apeel rate of 305 mm/minute (12 inches/minute). Stainless steel (SS) testpanels were prepared as described above. The cleaned panel was allowedto dry at room temperature. An adhesive coated film was cut into tapesmeasuring 1.27 cm×20 cm (½ in.×8 in.). A test sample was prepared byrolling the tape down onto a cleaned panel with 2 passes of a 2.0 kg(4.4 lb.) rubber roller. The prepared samples were dwelled at 23° C./50%RH for 15 minutes before testing. Four samples were tested for eachexample. The resulting peel adhesion was converted from ounces/0.5 inchto ounces/inch (N/dm) both values being reported in Tables 1-7.

Test Method 3: 90° Angle Peel Adhesion Test 2

For peel adhesion strength stainless steel (SS) substrates were cleanedas noted above. Two 1.0 inch (2.54 cm) by 3.0 inch (7.62 cm) strips ofadhesive were laminated to a 0.005 in. (127 micrometers) aluminum foilbacking for testing and were adhered to a stainless steel substrate(cleaned as described above) by rolling twice in each direction with a6.8 kg roller onto the tape at 12 inches per minute (305 mm/min). Theforce required to peel the tape at an angle of 90° was measured after a24 hour dwell at 25° C./50% humidity on an Instron (model number 4465,Instron Corporation, Norwood, Mass.). The measurements for the two tapesamples were in pound-force per inch with a platen speed of 12 inchesper minute (about 305 mm/min). The results were averaged and recorded inTable 8.

Test Method 4: Shear Strength Test 2

For shear strength a stainless steel (SS) backing was adhered to astainless steel (SS) substrate (cleaned as described above) using a 1.0inch (2.54 cm) by 0.5 inch (1.27 cm) square for 158° F. (70° C.)temperature shear testing. A weight of was 1 kg was placed on the samplefor 15 minutes. A 500 g load was attached to the tape sample fortesting. Each sample was suspended until failure and/or test terminated.The time to failure was recorded. Samples were run in triplicate andaveraged for Table 8 below.

Test Method 5—Determination of Yellowing

Isopropyl alcohol (IPA) was dispensed onto a 2 inch (5.08 cm) by 3 inch(7.62 cm) glass microscopic slide, wiped dry with a clean KIMWIPE tissuerepeated for a total of three washes with IPA and allowed to air dry. A2 inch (5.08 cm) by 3 (7.62 cm) inch strip of adhesive tape with arelease liner backing was adhered to the glass microscopic slide byrolling over the tape twice in each direction with a hand roller.Samples (with the protecting release liner removed) were then measuredon a CIELAB color scale for b* using a Ultrascanpro® spectrophotometer(HunterLab, Reston, Va.). Samples were measured under four conditionsand defined as follows:

-   -   1. Initial—adhesive measured with no UV or heat aging.    -   2. UV—adhesive exposed to 1.81 J/cm2 of UV A light from a Fusion        H bulb using a Model DRS-120 Fusion processor by Fusion UV        Systems, Inc., Gaithersburg, Md., and measured after 24 hrs of        UV exposure.    -   3. Heat—adhesive aged at 100° C. for 1 week in a Despatch LFD        Series oven and measured 24 hours after removal from oven    -   4. UV and Heat—combination of UV (2) followed by Heat (3)        Samples were run in triplicate and averaged results are        reported.

Test Method 6: 90° Angle Peel Adhesion Test 3 (Paper Surface)

A specimen measuring 1 in. (2.54 cm) wide and more than 3 in. (7.62 cm)long was cut in the machine direction from the test sample. The linerwas removed from one side of the adhesive and it was placed on analuminum panel measuring 2 in. by 5 in. (5.1 cm by 12.7 cm). The linerwas removed from the other side of adhesive and placed on a strip ofBoise copy paper (available from Packaging Corporation of America, LakeForest, Ill., USA) under the trade designation “X-9” (92 brightness, 24lb. (90 gsm/12M), 500 sheets, 8.5×11 (216 mm by 279 mm)) measuring 1 in.by more than 5 in. (2.54 cm by more than 12.7 cm) using light fingerpressure. The construction was then rolled once in each direction with astandard FINAT test roller 4.5 lb (2 kg) at a speed of approximately 12in./min. (305 mm/min). After applying the strips to the test panels, thepanel samples were allowed to dwell at constant temperature and humidity(25° C./50% RH) for 10 minutes before testing. The test panel and stripwere placed into a horizontal support. A jaw separation rate of 305mm/min. was used. Test results were measured in grams force/in. andconverted to Newtons/decimeter. The reported peel values are the averageof three 90° angle peel measurements.

All the examples tested were cleanly removable from the copy paperunless specified otherwise, meaning that the paper did not tear and alsodid not have any staining or residue after removal of the adhesive.

Test Method 7: Shear Test 3 (Dry Wall) Preparation of Drywall forTesting

The substrates employed were standard smooth drywall obtained from HomeDepot (Woodbury, Minn.). Knock-down and orange-peel drywall was preparedby IUPAT (International Union of Painters and Allied Trades, 3205Country Drive, Little Canada, Minn., USA). The drywall was primed usinga paint roller with Sherwin-Williams Pro-Mar 200. Surfaces were driedfor a minimum of 4 hours at ambient conditions before applying next coatof paint. White paint (Valspar Signature, Hi-def Advanced Color,Eggshell Interior, #221399, Ultra White/Base A) was applied to primeddrywall using a new paint roller and allowed to dry at ambientconditions until tackless before applying a second coat of the samecolor. The final painted drywall was dried overnight at ambientconditions and then placed into a 120° C. oven for 1 week. Samples wereremoved from oven and cut into desired dimensions using a draw knife.Samples were dusted off using KIMWIPE tissue, paper towels, or air (nocleaning with solvents) to remove dust left over from cutting before usein testing.

A standard static shear test was performed at elevated temperatureaccording to Pressure Sensitive Tape Council (Chicago, Ill.) PSTC-107(procedure G). The test was performed at 70° F./50% Relative Humidity.The sample area of adhesive bonded to the prepared drywall surface was 1in. (2.54 cm) in the vertical direction by 1 in. (2.54 cm) in the widthdirection (rather than 0.5 in. by 0.5 in. (1.27 cm by 1.27 cm) as calledfor by the method). Then a 6.8 kg weight was placed on top of the bondedsample area for 1 minute. After a dwell time of 60 seconds, the testspecimen was hung in the shear stand at desired temperature and loadedimmediately with a 250 g weight. The time to failure for the adhesivebond was recorded in minutes.

Test Method 8: Dynamic Mechanical Analysis

Examples 55 and 56 (0.025 in. (625 micrometers) thickness) were analyzedby Dynamic Mechanical Analysis (DMA) using a Discovery Hybrid parallelplate rheometer (TA Instruments, New Castle, Del.) to characterize thephysical properties of each sample as a function of temperature.Rheology samples were prepared by punching out a section of the PSA withan 8 mm circular die, removing it from the release liners, centering itbetween 8 mm diameter parallel plates of the rheometer, and compressinguntil the edges of the sample were uniform with the edges of the top andbottom plates. The furnace doors that surround the parallel plates andshafts of the rheometer were shut and the temperature was equilibratedat 20° C. and held for 1 minute. The temperature was then ramped from20° C. to 125 or 130° C. at 3° C./min while the parallel plates wereoscillated at an angular frequency of 1 Hertz and a constant strain of 5percent. The results are depicted in FIG. 1.

Test Method 9: 180° Angle Peel Adhesion Test 4 (Liner Release)

The 180 degree peel adhesion strength between the release liner andadhesive was measured for both sides of the liner: the “wet cast” side,also referred to herein as the “tight side release” where adhesive wasdirectly cast onto the release liner, and the “dry laminated”, alsoreferred to herein as the “easy side release where cured adhesive waslaminated to the release liner. Liner release strengths for both sideswas measured after aging for seven days at 23° C. and 50% relativehumidity. A 2.54 cm wide by approximately 20 cm in long sample of theadhesive transfer tape was cut using a specimen razor cutter. For tightside testing the sample was applied with its exposed adhesive surfacedown and lengthwise onto the platen surface of a peel adhesion tester(Model SP2000, IMASS Incorporated, Accord; MA). The adhesive transfertape was then rolled twice with a 2 kg rubber roller at a rate of 61cm/minute. The tight side release liner was carefully lifted away fromthe adhesive layer adhered to the platen surface, doubled-hack at anangle of 180 degrees, and secured to the clamp of the peel adhesiontester. The 180 degree angle release liner peel adhesion strength wasthen measured as the liner was peeled from the adhesive at a rate of 230cm/min (90 in/min). A minimum of two test specimens were evaluated withresults obtained in grams/inch which were used to calculate the averagerelease force. All release tests were carried out at 23° C. and 50%relative humidity (RH). For easy side testing two samples were appliedwith the first attached the platen surface and the second to the outerexposed (easy side) surface of the release liner covering the firstadhesive layer. The second sample was peeled away from the easy siderelease liner.

Test Method 10: 180° Angle Peel Adhesion Test 5 (Adhesive Strength)

Both faceside adhesion (i.e., the adhesive strength of the adhesivesurface in contact with the easy side release surface of the releaseliner) and backside adhesion (i.e., the adhesive strength of theadhesive surface in contact with the tight side release surface of therelease liner) were evaluated.

Stainless steel (SS) plates were prepared for testing by cleaning withone rinse of acetone followed by three rinses of heptane and drying.Adhesive transfer tape was used to prepare a single coated tape having a0.001 inch (25 micrometer) thick polyester backing. Two types of tapeswere prepared. The first had the adhesive joined to the backing by theadhesive surface that had been in contact with the tight side releasesurface of the release liner, resulting in an exposed adhesive surfacethat had been in contact with the easy side release surface of therelease liner. The second had the adhesive joined to the backing by theadhesive surface that had been in contact with the easy side releasesurface of the release liner, resulting in an exposed adhesive surfacethat had been in contact with the tight side release surface of therelease liner. As a result, the first tape sample was evaluated forfaceside adhesive strength and the second tape sample was evaluated forbackside adhesive strength.

The tape samples were 2.54 cm wide by 20 cm long (1 in. by 8 in.). Thesewere adhered to the stainless steel plates by means of the exposedadhesive, with 2.54 cm (1 in.) of length in contact with the plate, androlled down with two passes in each direction of a 2 kg rubber roller.The samples were allowed to dwell for 15 minutes at 23° C./50% RHfollowed by peel adhesion testing at an angle of 180° at a rate of 30.5cm/min (12 in./min) using an IMASS peel tester (described previously).The results were recorded in ounces/inch (oz/in) and also converted toNewtons/decimeter (N/dm).

Test Method 11: Overlap Shear Test 4

Flat, rigid, stainless steel plates were prepared for testing bycleaning with one rinse of acetone followed by three rinses of heptaneand drying. The adhesives to be tested were cut into strips measuring1.27 cm wide and 7.62 cm long, reinforced with 0.002 in (51 micrometer)aluminum foil and adhered by their exposed adhesive surface to thestainless steel plates with 2.54 cm (1 in.) of length and 1.27 cm (0.5in.) of width of each reinforced adhesive film strip in contact with theplate. A weight of 2 kilograms (4.4 pounds) was rolled twice over theadhered portion. Each of the resulting test specimens was equilibratedat room temperature for 15 minutes. Next, the specimens were transferredto a 70° C. oven, in which a 1000 gram or 500 gram weight was hung fromthe free end of the adhered film strip with the panel tilted 2° from thevertical. The time (in minutes) at which the weight fell, as a result ofthe adhesive film strip releasing from the plate, was recorded. The testwas discontinued at 10,000 minutes if there was no failure and theresult recorded as 10,000+ minutes. Two samples of each tape (adhesivefilm strip) were tested and the shear strength test results wereaveraged to obtain the reported shear values.

Materials

Material suppliers are listed with the first usage of the material. Ifnot specified, solvents and reagents can be obtained from Aldrich.Suppliers are listed in the examples as follows:

Aldrich—Sigma Aldrich, Milwaukee, Wis. Alfa—Alfa Aesar, Ward Hill, Mass.BASF—BASF Corporation, Florham Park, N.J. EMD—EMD Chemicals, Gibbstown,N.J. Dupont—E. I du Pont de Nemours and Company, Wilmington, Del.Mitsubishi—Mitsubishi Polyester Film Inc., Greer, S.C. TCI—TCI, Tokyo,Japan VWR—VWR International, LLC., Radnor, Pa.

2-Octyl Acrylate (2OA)—Prepared according to Preparatory Example 1 ofU.S. Pat. No. 7,385,020Iso-octyl Acrylate (IOA)—Obtained from 3M Company (St. Paul, Minn., USA)Acrylic Acid (AA)—Obtained from BASF Corporation (Florham Park, N.J.,USA)Isobornyl Acrylate (IBXA)—Obtained from San Esters Corporation (NewYork, N.Y., USA)Dicyclopentenyl Acrylate (DPA)—Obtained from Monomer-PolymerLaboratories (Windham, N.H., USA)Irgacure 651 (651)—Obtained from BASF Corporation (Florham Park, N.J.,USA)Irganox 1076 (1076)—Obtained from BASF Corporation (Florham Park, N.J.,USA)Regalrez 6108—Obtained from Eastman Chemical Corporation (Kingsport,Tenn., USA)

Preparatory Example 1 Citronellyl Acrylate (CiA)

A mixture of β-citronellol (300.00 g, 1.92 mol; Aldrich), hexane (1500mL), and triethylamine (212.49 g, 2.10 mol; Aldrich) was cooled in anice bath. Acryloyl chloride (190.08 g, 2.10 mol; Aldrich) was addeddropwise over 5 hours. The mixture was stirred for 17 hours at roomtemperature, and then filtered. The solution was concentrated undervacuum and washed with water. The solvent was removed under vacuum toprovide a crude oil that was purified by vacuum distillation. Acolorless oil (282.83 g of citronellyl acrylate) was collected at 70-75°C. at 0.30 mm Hg.

Preparatory Example 2 Geraniol Acrylate (GrA,[(2E)-3,7-dimethylocta-2,6-dienyl]prop-2-enoate)

A 2-liter round bottomed flask fitted with an overhead stirrer, anaddition funnel, and a condenser was charged with geraniol (195 g, 1.25mol; Alfa), triethylamine (152 g, 1.50 mol), and methylene chloride (500mL; EMD) and then cooled in an ice bath, and the mixture stirred. Asolution of acryloyl chloride (124 g, 1.38 mol;) in methylene chloride(100 mL) was added dropwise over a 45 minute period. When addition wascomplete, the ice bath was removed and the reaction mixture was stirredat room temperature overnight. The reaction mixture was filtered toremove the precipitated salts and washed 2 times with 150 mL portions ofa 10% solution of hydrochloric acid in water and 2 times with 150 mLportions of a saturated solution of sodium bicarbonate in water. Themethylene chloride solution was dried over potassium carbonate,filtered, and the solvent was removed at reduced pressure. Phenothiazine(50 mg, 0.2 mmol; TCI) was added and the product was distilled atreduced pressure. Product was collected at a boiling range of 87 to 92°C. and a pressure range of 0.50 to 0.65 mm. NMR analysis of thedistillate confirmed the structure as geraniol acrylate.

Preparatory Example 3 Farnesol Acrylate (FrA,[(2E,6E)-3,7,11-trimethyldodeca-2,6,10-trienyl]prop-2-enoate)

Farnesol acrylate was prepared as described in Preparatory Example 2except the reagents were farnesol (181 g, 0.81 mol; Alfa), triethylamine(99 g, 0.98 mol), methylene chloride (350 mL), and acryloyl chloride (81g, 0.90 mol) in methylene chloride (90 mL). The resulting product wasdistilled and collected at a boiling range of 112 to 118° C. and apressure range of 0.18 to 0.25 mm. NMR analysis of the distillateconfirmed the structure as farnesol acrylate.

Preparatory Example 4 3-Cyclohexene Methyl Acrylate (CMA)

A mixture of 3-cyclohexene methanol (95.00 g, 0.85 mol; Aldrich),methylene chloride (300 mL), and triethylamine (94.11 g, 0.93 mol; EMD)was cooled in an ice bath. Acryloyl chloride (84.17 g, 0.93 mol) wasadded dropwise over 4 hours. The mixture was stirred for 17 hours atroom temperature, then filtered. The solution was concentrated undervacuum, then diluted with ethyl acetate (500 mL; VWR). The solution waswashed with saturated aqueous sodium bicarbonate and brine, then driedover magnesium sulfate. The solvent was removed under vacuum to providea crude oil that was purified by vacuum distillation. A colorless oil(129.92 g of 3-cyclohexene methyl acrylate) was collected at 62-64° C.at 1.0 mm Hg.

Preparatory Example 5 Undecenyl Acrylate (UDA)

Undecenyl alcohol (69.66 g, 0.4090 mol; Alfa), toluene (300 mL), andtriethylamine (45.53 g, 0.45 mol) were added to a 1000 mL 3-necked roundbottomed flask. The solution was stirred and cooled to 0° C. in anitrogen atmosphere. Acryloyl chloride (40.73 g, 0.45 mol) was addeddropwise via addition funnel over a period of 4 hours. The cloudy yellowmixture was then slowly warmed to room temperature and placed on therotary evaporator to remove the toluene. Ethyl acetate (300 mL) wasadded and the mixture was filtered through celite, washed with saturatedsodium bicarbonate, and then the solvent was removed under vacuum. Thecrude yellow oil was purified by vacuum distillation. A faint yellow oil(55/75 g of 10-undecenyl acrylate) was collected at 90-96° C. @ 0.88 mmHg.

Preparatory Example 6 Oleyl Acrylate (OA)

A mixture of oleyl alcohol (90.00 g, 0.34 mol; Alfa), methylene chloride(300 mL), and triethylamine (38.45 g, 0.38 mol) was cooled in an icebath. Acryloyl chloride (34.89 g, 0.38 mol) was added dropwise over 2hours. The mixture was stirred for 17 hours at room temperature, thenfiltered. The solution was concentrated under vacuum. The crude oil wasloaded on a column of silica gel and eluted with hexane. The elutedsolution was collected and concentrated under vacuum to provide acolorless oily liquid (68.25 g of oleyl acrylate).

Brij 02 Acrylate was prepared according to US2012/0154811.

Examples 1-5 and Comparative Examples C1-C4

Compositions were prepared by charging a 500 mL jar with 270 g (90 wt.%) 2-octyl acrylate (2OA), 30 g (10 wt. %) of acrylic acid (AA; BASF),0.12 g (0.04 phr) of photoinitiator 1(2,2-dimethoxy-2-phenylacetophenone, Irgacure 651; BASF), and the amountin phr of one of the monofunctional acrylates (from the preparatoryexamples) as shown in Table 1. The monomer mixture was purged withnitrogen for 10 minutes then exposed to low intensity UV A light (lessthan 10 mW/cm², referred to as UV A because the output is primarilybetween 320 and 390 nm with a peak emission at around 350 nm which is inthe UV A spectral region) until a coatable syrup (Brookfield viscosityof 100-8000 cP) was formed, after which an additional 0.48 g (0.16 phr)of photoinitiator 1 was mixed into the composition.

The pre-adhesive (i.e. syrup) compositions were then coated on a releaseliner at a thickness of about 0.005 inches (127 micrometers) and curedunder a nitrogen atmosphere by further exposure to UVA light from 350 BLlight bulbs (40 watt, Osram Sylvania) as shown in Table 1 for varioustimes to form a pressure sensitive adhesive (PSA). Total energies weremeasured using a Powermap™ radiometer equipped with a low intensitysensing head (available from EIT Inc., Sterling, Va.). The PSA was thenlaminated under hand pressure with a small silicone roller to a primed0.002 inch (51 micrometer) thick poly(ethylene terepthalate) backing(trade designation Hostaphan 3SAB PET film; Mitsubishi Polyester Film,Incorporated, Greer, S.C.) to form a tape for adhesive testing.

Comparative Examples C1 and C2 were prepared as described above exceptthat no crosslinker was added to the prior to the syruping step. Theamounts of 1,6-hexanediol diacrylate (HDDA) was mixed into thepre-adhesive formulations before coating and curing.

Comparative Examples C3 and C4 were prepared as described in C1 and C2except that the crosslinker was2,4,-bis(trichloromethyl)-6-(3,4-dimethoxyphenyl)-triazine (T1).

The adhesives were tested for shear adhesion at 70° C., and 180° anglepeel adhesion. Results are shown in Table 1.

TABLE 1 180° Angle 70° C. Peel Adhesion Total UV Shear (min) to SS(oz/in, Crosslinker Exposure (Test N/dm) (Test Ex Material phr (g)mJ/cm² Method 1) Method 2) 1 CiA 0.6 1.8 2540 10,000+ 90.3, 98.6 2 CiA0.8 2.4 2540 10,000+  92.9, 101.6 3 CiA 1.0 3.0 2540 10,000+ 84.9, 92.94 GrA 0.6 1.8 1016 10,000+ 91.1, 99.7 5 FrA 0.6 1.8 1016  8264 85.1,93.1 C1 HDDA 0.1 0.3 1016  3432 41.3, 45.2 C2 HDDA 0.2 0.6 1016  589017.2, 18.8 C3 T1 0.1 0.3 593 10,000+ 79.1, 86.2 C4 T1 0.2 0.6 457210,000+ 74.3, 81.3

Examples 6-10, Comparative Examples C5-C8

Adhesive compositions and tapes were prepared and tested as described inExamples 1-5 except that 270 g (90 wt. %) of isooctyl acrylate (IOA)were used instead of 2OA and the crosslinkers in the amounts shown inTable 2 were used. Test results are shown in Table 2.

Adhesives tapes for Comparative Examples C5-C6 were prepared and testedas described in Comparative Examples C1-C2. Results are shown in Table2.

Adhesives tapes for Comparative Examples C7-C8 were prepared asdescribed in Comparative Examples C3-C4. Results are shown in Table 2.

TABLE 2 180° Angle 70° C. Peel Adhesion Total UV Shear (min) to SS(oz/in, Crosslinker Exposure (Test N/dm) (Test Ex Material phr (g)mJ/cm² Method 1) Method 2) 6 CiA 1.0 3.0 2535 10,000+ 66.9, 73.2 7 GrA0.8 2.4 2535 10,000+ 65.5, 71.7 8 GrA 1.0 3.0 2535 10,000+ 73.9, 80.8 9FrA 0.8 2.4 2535 10,000+ 70.3, 77.0 10  FrA 1.0 3.0 2535 10,000+ 66.5,72.8 C5 HDDA 0.1 0.3 2535  1463 68.9, 75.4 C6 HDDA 0.2 0.6 2535  348164.5, 70.6 C7 T1 0.1 0.3 2535 10,000+ 69.5, 76.0 C8 T1 0.2 0.6 253510,000+ 67.6, 74.0

Examples 11-25

Adhesive compositions were prepared by charging an 8 ounce jar with 45 gof IOA, 5 g of AA, 0.02 g of photoinitiator 1 and the amounts and typeof monofunctional acrylates (from preparatory examples) as shown inTable 3. The monomer mixture was purged with nitrogen for 5 minutes thenexposed to UV A light from a low intensity black bulb (15 watt, 365 nmpeak) until the viscosity increased and a coatable syrup was prepared.

An additional 0.08 g (0.16 phr) of the photoinitiator 1 was mixed intothe syrup. The compositions were then knife-coated between two clearrelease liners at a 0.005 inch (127 micrometers) thickness and cured byexposure to UV A light from 350 BL light bulbs (40 watt, Osram Sylvania)as shown in Table 3. Total UV exposure was measured with an Uvirad® LowEnergy UV Integrating Radiometer (EIT, Inc., Sterling, Va.). Tapes wereprepared as described in Examples 1-5, and tested for shear and peeladhesion. Results are shown in Table 3.

TABLE 3 180° Angle 70° C. Peel Adhesion Total UV Shear (min) to SS(oz/in, Crosslinker Exposure (Test N/dm) (Test Ex Material phr (g)mJ/cm² Method 1) Method 2) 11 CiA 2.0 1.0 2189 10,000+ 60.3, 66.0 12 CiA5.0 2.5 2189 10,000+ 43.1, 47.2 13 CiA 10.0 5.0 2189 10,000+ 27.1, 29.614 GrA 2.0 1.0 2189 10,000+ 66.7, 73.0 15 GrA 5.0 2.5 2189 10,000+ 44.2,48.4 16 GrA 10.0 5.0 2189 10,000+ 23.4, 25.6 17 FrA 2.0 1.0 2189 10,000+51.7, 56.6 18 FrA 5.0 2.5 2189 10,000+ 40.7, 44.5 19 FrA 10.0 5.0 218910,000+ 26.7, 29.2 20 UDA 1.0 0.5 1712 10,000+ 51.2, 56.0 21 UDA 5.0 2.51712 10,000+ 21.7, 23.7 22 CMA 1.0 0.5 1712  1092 75.6, 82.7 23 CMA 5.02.5 1712 10,000+ 68.2, 74.6 24 OA 1.0 0.5 1186 10,000+ 74.6, 81.6 25 OA5.0 2.5 1186 10,000+ 60.0, 65.6 26 Brij O2 A 1.0 0.5 1500  2098 76.1,83.2 27 Brij O2 A 5.0 2.5 1500 10,000+ 61.4, 67.1

Examples 28-33

Adhesives and tapes were prepared and tested as described in Examples11-27 except that the monofunctional acrylate crosslinker was not addedto the syrup composition, but mixed in prior to coating and curing. Theamounts of crosslinker and test results are shown in Table 4.

TABLE 4 180° Angle 70° C. Peel Adhesion Total UV Shear (min) to SS(oz/in, Crosslinker Exposure (Test N/dm) (Test Ex Material phr (g)mJ/cm² Method 1) Method 2) 28 CiA 1.0 0.5 1422 10,000+ 62.7, 68.6 29 CiA2.0 1.0 1422 10,000+ 51.2, 56.0 30 GrA 1.0 0.5 1422 10,000+ 69.1, 75.631 GrA 2.0 1.0 1422 10,000+ 54.9, 60.1 32 FrA 1.0 0.5 1422 10,000+ 66.0,72.2 33 FrA 2.0 1.0 1422 10,000+ 52.9, 57.9

Examples 34-39

Compositions for Examples 34-37 were prepared by charging a 500 mL jarwith 467.5 g (93.5 wt. %) of IOA, 32.5 g (6.5 wt. %) of AA, 0.2 g (0.04phr) of photoinitiator 2 (trade designation Irgacure 184; BASF), and theamounts of CiA shown in Table 5. The monomer mixture was purged withnitrogen for 5-10 minutes then exposed to low intensity UV A radiationuntil a coatable syrup was formed.

An additional 1.75 g (0.16 phr) of photoinitiator 2 and 50 g (10 phr) oftackifier (trade designation Foral 85LB, Eastman Chemical Co.,Kingsport, Tenn.) were then mixed into each composition. Thecompositions were then coated onto a release liner at 0.004 inch (101.6micrometer) thickness and cured under a nitrogen atmosphere by exposureto UV A light from 350 BL light bulbs (40 watt, Osram Sylvania) followedby exposure to high intensity UV C light (greater than 10 mW/cm²,referred to as UV C because the output of the bulbs is nearlymonochromatic between 250 and 260 nm in the UV C spectral region) toform a PSA. Total UV exposure was measured as described for Examples 1-5and is shown in Table 5. Tapes were prepared as in Examples 1-5 foradhesive testing.

Compositions and tapes for Example 38 were prepared and tested in thesame manner as Example 35 except that 2OA was used instead of IOA. Testresults for all tapes are shown in Table 5.

Compositions and tapes for Example 39 were prepared and tested as inExample 35 except the tackifier was trade designation Regalrez 6108(Eastman Chemical Co., Kingsport, Tenn.) instead of trade designationForal 85LB.

TABLE 5 180° Angle Total UV 70° C. Peel Adhesion Exposure Shear (min) toSS (oz/in, Crosslinker mJ/cm² (Test N/dm) (Test Ex Material phr (g)(UVA + UVC) Method 1) Method 2) 34 CiA 2 10 854 + 276 10,000+ 59.5, 65.135 CiA 3 15 854 + 276 10,000+ 49.6, 54.3 36 CiA 5 25 909 + 252 10,000+25.1, 27.5 37 CiA 10 50 909 + 252 10,000+ 18.0, 19.7 38 CiA 3 15 909 +252 10,000+ 43.8, 47.9 39 CiA 3 15 880 + 237 10,000+ 45.1, 49.3

Examples 40-42

Compositions were prepared by charging a 500 mL jar with 420.8 g (93.5wt %) of IOA, 29.3 (6.5 wt %) g of AA, 0.18 g (0.04 phr) of photoiniator2 (trade designation Irgacure 184), and the amounts of CiA shown inTable 6. The monomer mixture was purged with nitrogen for 5-10 minutesthen exposed to low intensity ultraviolet radiation until a coatablesyrup was prepared.

An additional 1.58 g (0.16 phr) of photoinitiator 2, 45 g (10 phr) oftackifier (trade designation Foral 85LB), and the amounts of triazine T2(2,4,-bis(trichloromethyl)-6-(4-methoxy)phenyl)-triazine) shown in Table6 were mixed into the composition. The pre-adhesive (syrup) formulationswere then coated onto a release liner at 0.004 inch (101.6 micrometer)thickness and cured under a nitrogen atmosphere by exposure to 883mJ/cm² of UV A light from 350 BL light bulbs (40 watt, Osram Sylvania).Total UV exposure was measured as described in Examples 1-5. The PSA wasthen laminated under hand pressure with a small silicone roller to aprimed poly(ethylene terepthalate) (Polyester Films, Incorporated,Greer, S.C.) film backing for adhesive testing.

TABLE 6 180° Angle 70° C. Peel Adhesion Shear (min) to SS (oz/in,Crosslinker (CiA/T2) (Test N/dm) (Test Ex Material phr (g) Method 1)Method 2) 40 CiA and T2 0.8/0.11 3.38/0.51 10,000+ 60.9, 66.6 41 CiA andT2 1.5/0.08 6.75/0.34 10,000+ 54.2, 59.3 42 CiA and T2 2.3/0.0410.13/0.17  10,000+ 48.5, 53.1

Examples 43-46

Compositions for Examples 43-45 were prepared by charging a 500 mL jarwith 346.9 g (82.6 wt %) of IOA, 3.2 g (0.1 wt %) of AA, 0.14 g (0.04phr) of photoinitiator1, and the amounts of CiA shown in Table 7. Themonomer mixture was purged with nitrogen for 5-10 minutes then exposedto low intensity ultraviolet radiation to form a coatable syrup.

An additional 0.84 g (0.16 phr) of photoinitiator1, 0.26 g ofantioxidant (Irganox 1076), 70 g (17 wt. %) of isobornyl acrylate(IBXA), and 100.8 g (24 phr) of tackifiers (trade designation Regalrez6108) were added. The compositions were mixed thoroughly by rollingovernight and coated onto release liner at 5 mil (127 micrometer)thickness and cured under a nitrogen atmosphere by exposure to 827mJ/cm² of UV A light followed by exposure to 236 mJ/cm² UV C light toform a PSA as described in Examples 34-39. Total UV exposure wasmeasured as described in Examples 1-5. The PSA was then laminated to aprimed poly(ethylene terepthalate) (Mitsubishi Polyester Films) backingfor adhesive testing. Results are shown in Table 7.

Compositions and tapes for Example 46 were prepared using 2OA instead ofIOA.

TABLE 7 180° Angle Peel 70° C. Shear Adhesion to SS Crosslinker (min)(oz/in, N/dm) Ex Material phr (g) (Test Method 1) (Test Method 2) 43 CiA3 10.5 19 71.6, 78.3 44 CiA 5 17.5 159  49.0, 53.6 45 CiA 10 35.010,000+   25.8, 28.2 46 CiA 3 10.5 63 71.8, 78.5

Examples 47-48 and Comparative Examples C9-C10

Example 47 was prepared by charging a 500 mL jar with 306.3 g (87.5 wt.%) IOA, 43.8 g (12.5 wt. %) of AA, 0.14 g (0.04 phr) of photoinitiator1, and 2.1 g (0.6 phr) of CiA. The monomer mixture was purged withnitrogen for 10 minutes then exposed to low intensity UV A radiationuntil a coatable syrup was formed, after which another 0.67 g (0.16 phr)of photoinitiator1 was added. Next, 6.0 g (1.7 phr) of trade designationHDK H15 fumed silica (Wacker Silicones) were added and the syrup wasmixed with a trade designation Netzsch Model 50 Dispersator. When thefumed silica was completely dispersed, 28 g (8 phr) of glass bubbles(K15, 3M Company, St. Paul Minn.) were added and the composition wasmixed thoroughly by rolling overnight.

The composition was then coated between release liners at a 0.038 inch(965.2 micrometers) thickness and cured by 741 mJ/cm² of UV A light from350 BL light bulbs (40 watt, Osram Sylvania) to form a PSA. Total UVexposure was measured as described in examples 1-5.

A composition and tape Example C9 were prepared as in Example 47 exceptthat no CiA was added to the syrup composition, and 0.19 g (0.055 phr)HDDA was added to the syrup before coating.

A composition and tape for Example 48 were prepared as in Example 47except the composition for the syrup was 315 g (90 wt. %) of 2OA, 35 g(10 wt %) of AA, 0.14 g (0.04 phr) of photoinitiator 1, and 3.5 g (1phr) of CiA.

A composition and tape for Example C10 were prepared as in Example C9except using the composition of Example 48.

Example 47-48 and C₉₋₁₀ were prepared for adhesive testing and tested asoutlined in the test methods 3 and 4.

TABLE 8 90° Peel Adhe- 70° C. Shear sion to SS Backbone (min) (lbf-in,kg-cm) Ex Monomer Crosslinker/phr (Test Method 4) (Test Method 3) 47 IOA CiA/0.6 10,000+ 23.5, 27.1 48 2OA CiA/1  10,000+ 19.2, 22.1 C9  IOAHDDA/0.055 10,000+ 23.1, 26.6 C10 2OA HDDA/0.055 10,000+ 22.4, 25.8

Adhesive samples from Examples 3, 35-38, 40-42, and 45, and C3 weremeasured for yellowing as described above. Results are shown in Table 9.

TABLE 9 Adhesive b* UV Ex Thickness (mil) b* Initial b* UV b* Heat &Heat  3 5 0.21 0.33 0.36 0.73 35 4 0.22 0.42 0.69 1.29 36 4 0.23 0.300.68 1.13 37 4 0.25 0.32 0.63 0.91 38 4 0.23 0.45 0.68 1.11 40 4 0.871.28 1.38 2.05 41 4 0.67 0.93 0.98 1.50 42 4 0.44 0.52 0.77 1.11 45 50.21 0.32 0.30 0.59 C3 (T1) 5 0.76 1.33 1.14 1.98

Examples 49-52 and C11

Adhesive composition and tape 49 was made by charging a glass bottlewith 54 g (90 wt. %) 2OA, 6 g (10 wt. %) of AA, 0.6 g (1 phr) CiA, 0.06g (0.1 phr) of Vazo 52 (Dupont), and 140 g ethyl acetate. This mixturewas purged with nitrogen gas for 20 minutes, and the bottle was sealedand placed in a water bath at 52° C. with shaking for 20 hours. Thebottle was then removed, and sparged with air for 1 minute. 30 g of thefinal polymer solution was combined in a jar with 0.17 g (2 phr) ofphotoinitiator 1 and rolled to ensure thorough mixing. The compositionwas then coated at 0.005 inch (127 micrometers) thickness on a 0.002inch (51 micrometer) thick Mitsubishi Hostaphan 3SAB PET polyester film,and dried in an oven at 70° C. for 30 minutes. The dried adhesive wascovered with a release liner and exposed to 982 mJ/cm² of UVA light over10 minutes. Adhesive testing was then carried out according to testmethods 1 and 2 except the shear strength test was carried out at roomtemperature rather than 70° C. Results are shown in Table 10.

Adhesive composition and tape 50 was made and tested in the same manneras example 46 except that the composition was 90 g (90 wt. %) 2OA, 10 g(10 wt. %) of AA, 2 g (2 phr) CiA, 0.04 g (0.04 phr) isooctylthioglycolate, 0.1 g (0.1 phr) of Vazo 67 (Dupont), and 233.3 g ethylacetate, and the cure was carried out with 762 mJ/cm² of UVA light over10 minutes.

Adhesive composition 51 was made and tested in exactly the same way ascomposition 49 except that no photoinitiator was added. Adhesivecomposition 52 was made in exactly the same way as composition 50 exceptthat no photoinitator was added.

Adhesive composition and tape C11 was made and tested in the samefashion as Example 49 except that the composition contained no CiA, andthe cure was carried out with 2011 mJ/cm² of UVA light over 10 minutes.

TABLE 10 RT Shear 180° Angle (min) Peel Adhesion Photo- (Modified to SS(oz/in, Crosslinker initator 1 Test N/dm) (Test Ex Material phr (g) phrg Method 1) Method 2) 49 CiA 1 0.6 2 0.17 5,246 50.3, 55.1 50 CiA 2 2 20.17 5,285 58.9, 64.5 51 CiA 1 0.6 0 0 135 54.6, 59.8 52 CiA 2 2 0 0 34271.4, 78.2 C11 N/A N/A N/A 2 0.17 880 40.7, 44.6

Examples 53-56

Examples 53 and 54 were prepared by charging a 500 mL jar with 350 g(100 wt. %) 2OA, 0.14 g (0.04 phr) of photoinitiator 1, and a quantityof CiA according to Table 11. The monomer mixture was purged withnitrogen for 10 minutes then exposed to low intensity UVA radiationuntil a coatable syrup was formed, after which another 0.67 g (0.16 phr)of photoinitiator 1 was added. Next, 6.0 g (1.7 phr) of HDK H15 fumedsilica (Wacker Silicones) was added and the syrup was mixed with aNetzsch Model 50 Dispersator. When the fumed silica was completelydispersed, 28 g (8 phr) of glass bubbles (K15, 3M Company, St. PaulMinn.) were added and the composition was mixed thoroughly by rollingovernight.

The composition was then coated at a 0.025 inch (635 micrometers)thickness between a release liner and a primed 0.002 inch (51micrometer) polyethylene terepthalate (PET) and cured by a dose of UV Alight (shown in Table 11) from 350 BL light bulbs (40 watt, OsramSylvania) to form a PSA. Total UV exposure was measured as described inexamples 1-5. Adhesive properties were tested according to test methods6 and 7 and are shown in Table 11.

Examples 55 and 56 were made as described above except for thefollowing 1) the initial composition contained 300 g (100 wt. %) 2OA,0.12 g (0.04 phr) of photoinitiator 1, and a quantity of CiA accordingto Table 11, 2) 0.57 g (0.16 phr) of photoinitiator 1, 5.1 g (1.7 phr)of HDKH15 fumed silica, and 24 g (8 phr) of glass bubbles were addedafter the prepolymer syrup was prepared. For rheological measurements,the coatable syrup was coated at 0.025 inch (635 micrometer) thicknessand cured in the same manner.

TABLE 11 70° C. Shear to 90° Angle Orange Peel Peel Adhesion Dry Wall toPaper (lb-in, Backbone CiA CiA UV Dose (min.) (Test kg-cm) (Test ExMonomer (g) (phr) (mJ/cm²) Method 7) Method 6) 53 2OA 1.75 0.5 1482  275 4821.3, 5554.6 54 2OA 3.5 1.0 1482 10,000+ 3611.9, 4161.3 55 2OA4.11 1.37 2664 10,000+ 2677.5, 3084.7 56 2OA 5.49 1.83 2664  87902211.9, 2448.3

Examples 57-60

Adhesive compositions and tapes 57-60 were made and tested in exactlythe same way as examples 11-25. The crosslinkers employed and adhesiveproperties are shown in Table 12. Dicyclopentenyl acrylate (DPA) wasobtained from Monomer-Polymer Laboratories (Windham, N.H., USA).Ethylene glycol dicyclopentenyl ether acrylate (EGDA) was obtained fromAldrich.

TABLE 12 180° Peel 70° C. Adhesion to Total UV Shear (min) SS (oz/in,Crosslinker Exposure (Test N/dm) (Test Ex Material phr (g) mJ/cm²Method 1) Method 2) 57 EGDA 0.5 0.25 2102 1,826  92.2, 100.9 58 EGDA 1.00.5 2102 10,000+ 82.1, 89.9 59 DPA 0.5 0.25 1934 2,246 83.3, 91.2 60 DPA1.0 0.5 1934 10,000+ 85.8, 93.9

TABLE 13 Low Tg High Tg Monomer Monomer Fumed Glass (2OA or (AA and/orCrosslinking Tackifier Silica Bubbles Example IOA) wt-% IBXA) wt-%Monomer wt- % wt-% wt-% wt-% 34 83.2 5.8 CiA - 1.8 8.9 0 0 35 82.5 5.7CiA - 2.6 8.8 0 0 36 81.0 5.6 CiA - 4.3 8.7 0 0 37 77.7 5.4 CiA - 8.38.3 0 0 38 82.5 5.7 CiA - 2.6 8.8 0 0 39 82.5 5.7 CiA - 2.6 8.8 0 0 4084.0 5.9 CiA/T2 - 0.7/0.1 9.0 0 0 41 83.5 5.8 CiA/T2 - 1.3/0.07 8.9 0 042 83.0 5.8 CiA/T2 - 2.0/0.03 8.9 0 0 43 65.2 13.7 CiA - 2.0 18.9 0 0 4464.3 13.6 CiA - 3.2 18.7 0 0 45 62.3 13.1 CiA - 6.3 18.1 0 0 46 65.213.7 CiA - 2.0 18.9 0 0 47 79.1 11.3 CiA - 0.5 0 1.6 7.2 48 81.1 9.0CiA - 0.9 0 1.5 7.2 53 90.5 0 CiA - 0.5 0 1.6 7.2 54 90.1 0 CiA - 0.9 01.5 7.2 55 89.8 0 CiA - 1.2 0 1.5 7.2 56 89.5 0 CiA - 1.6 0 1.5 7.2

Pressure Sensitive Adhesive (PSA) A

PSA A was made by charging a gallon jar with 1) 1620 g of 2OA, 2) 180 gof AA, 3) 0.72 g (0.04 phr) of 651, and 4) 36 g of citronellyl acrylate(CiA). The monomer mixture was purged with nitrogen for 10 minutes thenexposed to low intensity ultraviolet radiation until a coatable syrupwas obtained. An additional 2.7 g (0.15 phr) of 651 was then added. Thepre-adhesive formulation were then coated onto either release liner A orB at 0.002 inches (51 micrometers) thickness and cured under nitrogen byexposure to 366 mJ/cm² of UV A light over 43 seconds and 113 mJ/cm² ofUVC light over 15 seconds.

Pressure Sensitive Adhesive (PSA) B PSA B was made by charging a gallonjar with 1) 1620 g of 2OA, 2) 180 g of AA, 3) 0.72 g (0.04 phr) of 651,and 4) 36 g of dicyclopentyl acrylate (DPA). The monomer mixture waspurged with nitrogen for 10 minutes then exposed to low intensityultraviolet radiation until a coatable syrup was obtained. An additional2.7 g (0.15 phr) of 651 was then added. The pre-adhesive formulationwere then coated onto either release liner A or B at 0.002 inches (51micrometers) thickness and cured under nitrogen by exposure to 366mJ/cm² of UV A light over 43 seconds and 113 mJ/cm² of UVC light over 15seconds.

Pressure Sensitive Adhesive (PSA) C

PSA C was made by charging a gallon jar with 1) 1784 g 2OA, 2) 16.2 g ofAA, 3) 0.72 g of 651, and 4) 54 g of CiA. The monomer mixture was purgedwith nitrogen for 10 minutes then exposed to low intensity ultravioletradiation until a coatable syrup was obtained. An additional 4.3 g (0.24phr) of 651, 360 g of IBXA, 1.35 g of 1076, and 518.4 g of Regalrez 6108were then added. The pre-adhesive formulations were then coated ontorelease liner A at 0.002 inches (51 micrometers) thickness and curedunder nitrogen by exposure to 884 mJ/cm² of UV A light over 3 minutes.

Pressure Sensitive Adhesive (PSA) D

PSA D was made by charging a gallon jar with 1) 1784 g 2OA, 2) 16.2 g ofAA, 3) 0.72 g of 651, and 4) 54 g of DPA. The monomer mixture was purgedwith nitrogen for 10 minutes then exposed to low intensity ultravioletradiation until a coatable syrup was obtained. An additional 4.3 g (0.24phr) of 651, 360 g of IBXA, 1.35 g of 1076, and 518.4 g of Regalrez 6108were then added. The pre-adhesive formulations were then coated ontorelease liner A at 0.002 inches (51 micrometers) thickness and curedunder nitrogen by exposure to 884 mJ/cm² of UV A light over 3 minutes.

Release Liner (RL) A

A 0.002 in. (51 micrometer) thick polyester film having a siliconeacrylate release coating on both sides was prepared using the processdescribed in Example 61 of US 2013059105.

Release Liner (RL) B

A 0.004 in. (51 micrometer) thick, 58 pound polycoated Kraft paperrelease liner having a silicone acrylate release coating on both sideswas prepared using the process described in Example 61 of US 2013059105.

Examples 61-66

The various combinations of pressure sensitive adhesives and releaseliners shown in Table 14 were evaluated for faceside (FS) and backside(BS) peel adhesion strengths as describe in Test Method 10: 180° AnglePeel Adhesion Test 5 (Adhesive Strength). Construction were alsoprepared and evaluated for release liner peel strengths as described inTest Method 9: 180° Angie Peel Adhesion Test 4 (Liner Release). Theresults are shown in Table 14. Release values and release ratios werealso observed to remain relatively stable even after aging for 7 days at70° C., as well as for 7 days at 90% RH and 32° C. (90° F. In addition,Examples 61-66 all exhibited overlap shear values of more than 10,000minutes when evaluated according to Test Method 11: Overlap Shear Test4.

TABLE 14 FS Peel Adhe- BS Peel Adhe- Easy Side Tight Side Release sionto SS sion to SS Release Release Ratio Ex. PSA RL (oz/in, N/dm) (oz/in,N/dm) (g/in, g/cm) (g/in, g/cm) (Tight/Easy) 61 A A 34.0, 37.2 39.1,42.8 6.5, 2.6 28.8, 11.3 4.43 62 B A 45.2, 49.5 41.3, 45.2 5.7, 2.224.1, 9.5  4.23 63 A B 41.5, 45.4 39.5, 43.2 8.9, 3.5 58.4, 23.0 6.56 64B B 48.0, 52.5 40.0, 43.8 7.7, 3.0 50.9, 20.0 6.61 65 C A 37.8, 41.440.2, 44.0 9.4, 3.7 32.4, 12.8 3.45 66 D A 36.9, 40.4 48.2, 52.8 6.6,2.6 26.4, 10.4 4.00

What is claimed is:
 1. An article comprising a release liner and apressure sensitive adhesive composition disposed on a major surface ofthe release liner, wherein the pressure sensitive adhesive comprises atleast 50 wt-% of polymerized units derived from alkyl(meth)acrylatemonomer(s); and 0.2 to 15 wt-% of at least one crosslinking monomercomprising a (meth)acrylate group and a C₆-C₂₀ olefin group, the olefingroup being straight-chained or branched and optionally substituted. 2.The article of claim 1 wherein the pressure sensitive adhesive comprisesat least 55, 60, 65, or 70 wt-% of polymerized units derived from one ormore alkyl(meth)acrylate monomer(s).
 3. The article of claim 1 whereinthe crosslinking monomer has the formula:

R1 is H or CH₃, L is an optional linking group; and R2 is an optionallysubstituted C₆-C₂₀ olefin group.
 4. The article of claim 3 wherein Lcomprises one or more alkylene oxide groups.
 5. The article of claim 3wherein the crosslinking monomer is selected from the group consistingof citronellyl(meth)acrylate, geraniol(meth)acrylate,farnesol(meth)acrylate, undecenyl(meth)acrylate, andoleyl(meth)acrylate.
 6. The article of claim 1 wherein the pressuresensitive adhesive composition comprises at least 50, 55, 60, 65, or 70wt-% of polymerized units of alkyl(meth)acrylates comprising 6 to 20carbon atoms.
 7. The article of claim 1 wherein the pressure sensitiveadhesive comprises a bio-based content of at least 25% of the totalcarbon content.
 8. The article of claim 1 wherein the pressure sensitiveadhesive comprises polymerized units derived from 2-octyl(meth)acrylate.9. The article of claim 1 wherein the pressure sensitive adhesivefurther comprises filler.
 10. The article of claim 9 wherein the fillercomprises fumed silica, glass bubbles, or a combination thereof.
 11. Thearticle of claim 1 wherein the pressure sensitive adhesive compositionfurther comprises a tackifier.
 12. The article of claim 1 wherein thepressure sensitive adhesive composition further comprises polymerizedunits derived from at least one monomer selected from acid-functionalmonomers, non-acid functional polar monomers, vinyl monomers, andcombinations thereof.
 13. The article of claim 1 wherein the pressuresensitive adhesive further comprises a multifunctional (meth)acrylatecrosslinker, a triazine crosslinker, or a combination thereof.
 14. Thearticle of claim 1 wherein the pressure sensitive adhesive exhibits a180° degree peel adhesion to stainless steel of at least 15 N/dm aftercuring.
 15. The article of claim 1 wherein the pressure sensitiveadhesive composition comprises 0 to 1.0 wt-% of polymerized unitsderived from acid-functional monomers.
 16. The article of claim 1wherein the pressure sensitive adhesive composition comprises 0 to 10wt-% of polymerized units derived from high Tg monomers.
 17. The articleof claim 1 wherein the release liner is created by applying a layercomprising a (meth)acrylate-functional siloxane to a major surface of asubstrate; and irradiating said layer, in a substantially inertatmosphere comprising no greater than 500 ppm oxygen, with a shortwavelength polychromatic ultraviolet light source having at least onepeak intensity at a wavelength of from about 160 nanometers to about 240nanometers to at least partially cure the layer, optionally wherein thelayer is at a curing temperature greater than 25° C.
 18. The article ofclaim 17 wherein the at least one peak intensity is at a wavelengthbetween about 170 nanometers to about 220 nanometers.
 19. The article ofclaim 18 wherein the peak intensity is at a wavelength of about 185nanometers.
 20. The article of claim 17 wherein the short wavelengthpolychromatic ultraviolet light source comprises at least one lowpressure mercury vapor lamp, at least one low pressure mercury amalgamlamp, at least one pulsed Xenon lamp, at least one glow discharge from apolychromatic plasma emission source, or combinations thereof.
 21. Thearticle of claim 17 wherein the layer consists essentially of one ormore (meth)acrylate-functional siloxane monomers.
 22. The article ofclaim 17 wherein the layer consists essentially of one or more(meth)acrylate-functional siloxane oligomers.
 23. The article of claim17 wherein the layer consists essentially of one or more(meth)acrylate-functional polysiloxanes.
 24. The article of claim 17wherein the layer further comprises one or more copolymerizablematerials selected from the group consisting of monofunctional(meth)acrylate monomers, difunctional (meth)acrylate monomers,polyfunctional (meth)acrylate monomers having functionality greater thantwo, vinyl ester monomers, vinyl ester oligomers, vinyl ether monomers,and vinyl ether oligomers.
 25. The article of claim 17 wherein the layerfurther comprises at least one functional polysiloxane material whichdoes not comprise a (meth)acrylate functionality.
 26. The article ofclaim 25 wherein the functional polysiloxane material is selected fromat least one a vinyl-functional polysiloxane, a hydroxy-functionalpolysiloxane, an amine-functional polysiloxane, a hydride-functionalpolysiloxane, an epoxy-functional polysiloxane, and combinationsthereof.
 27. The article of claim 17 wherein the layer further comprisesat least one non-functional polysiloxane material.
 28. The article ofclaim 27 wherein the at least one non-functional polysiloxane materialis selected from at least one of a poly(dialkylsiloxane), apoly(alkylarylsiloxane), a poly(diarylsiloxane), apoly(dialkyldiarylsiloxane), or a combination thereof, optionallywherein the non-functional polysiloxane material comprises from 0.1 wt.% to 95 wt. %, inclusive, of the at least partially cured layer.
 29. Thearticle of claim 17 wherein the layer is substantially free of an addedphotoinitiator.
 30. The article of claim 17 wherein the layer issubstantially free of an organic solvent.
 31. The article of claim 17wherein the substantially inert atmosphere comprises no greater than 50ppm oxygen.
 32. The article of claim 17 wherein applying the layer tothe surface of the substrate comprises applying a discontinuous coating.33. The article of claim 17 wherein the layer is substantially free ofmetal catalyst.
 34. An article comprising a release liner and a pressuresensitive adhesive composition disposed on a major surface of therelease liner, wherein the pressure sensitive adhesive is a UV curable(meth)acrylic pressure sensitive adhesive that is substantially free ofhalogens, and further wherein the release liner comprises a UV curablerelease layer on a major surface of a substrate.
 35. The article ofclaim 34 wherein the release layer comprises a (meth)acrylate-functionalsiloxane.
 36. The article of claim 34 wherein the release liner isderived by applying a layer comprising a (meth)acrylate-functionalsiloxane to a major surface of a substrate; and irradiating said layer,in a substantially inert atmosphere comprising no greater than 500 ppmoxygen, with a short wavelength polychromatic ultraviolet light sourcehaving at least one peak intensity at a wavelength of from about 160nanometers to about 240 nanometers to at least partially cure the layer,optionally wherein the layer is at a curing temperature greater than 25°C.
 37. The article of claim 34 wherein the pressure sensitive adhesivecomprises a bio-based content of at least 25% of the total carboncontent.
 38. An article comprising a release liner and a pressuresensitive adhesive composition disposed on a major surface of therelease liner, wherein the pressure sensitive adhesive comprises atleast 50 wt-% of polymerized units derived from alkyl(meth)acrylatemonomer(s); and 0.2 to 15 wt-% of at least one crosslinking monomercomprising a (meth)acrylate group and a C₆-C₂₀ olefin group, the olefingroup being straight-chained or branched and optionally substituted, andfurther wherein the release liner is derived by applying a layercomprising a (meth)acrylate-functional siloxane to a major surface of asubstrate; and irradiating said layer, in a substantially inertatmosphere comprising no greater than 500 ppm oxygen, with a shortwavelength polychromatic ultraviolet light source having at least onepeak intensity at a wavelength of from about 160 nanometers to about 240nanometers to at least partially cure the layer, optionally wherein thelayer is at a curing temperature greater than 25° C.
 39. The article ofclaim 38 wherein the pressure sensitive adhesive comprises a bio-basedcontent of at least 25% of the total carbon content.